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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Nov. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	BL
Entity Registrant Name	BLACKLINE, INC.
Entity Central Index Key	0001666134
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		52,851,442

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 24,645	$ 22,118
Marketable securities	85,125	83,130
Accounts receivable, net	45,233	42,294
Deferred sales commissions	10,946	9,667
Prepaid expenses and other current assets	6,794	6,614
Total current assets	172,743	163,823
Capitalized software development costs, net	6,129	4,591
Property and equipment, net	12,126	11,318
Intangible assets, net	44,130	54,118
Goodwill	185,138	185,138
Other assets	1,857	1,449
Total assets	422,123	420,437
Current liabilities:
Accounts payable	2,934	7,165
Accrued expenses and other current liabilities	18,354	18,931
Deferred revenue	94,158	80,360
Short-term portion of contingent consideration	2,008	2,008
Total current liabilities	117,454	108,464
Common stock warrant liability		11,380
Contingent consideration	3,597	3,230
Deferred tax liabilities, net	993	1,262
Deferred revenue, noncurrent	2,100	2,373
Other long-term liabilities	2,190	2,318
Total liabilities	126,334	129,027
Commitments and contingencies (Note 6)
Stockholders' equity:
Common stock	528	513
Additional paid-in capital	414,915	378,272
Accumulated other comprehensive loss	(32)	(41)
Accumulated deficit	(119,622)	(87,334)
Total stockholders' equity	295,789	291,410
Total liabilities and stockholders' equity	$ 422,123	$ 420,437

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Subscription and support	$ 43,462	$ 30,853	$ 120,757	$ 83,830
Professional services	2,409	1,343	6,041	3,953
Total revenues	45,871	32,196	126,798	87,783
Cost of revenues
Subscription and support	8,707	6,440	24,729	18,515
Professional services	2,191	1,101	5,776	3,029
Total cost of revenues	10,898	7,541	30,505	21,544
Gross profit	34,973	24,655	96,293	66,239
Operating expenses
Sales and marketing	33,375	19,037	81,996	56,279
Research and development	5,883	5,087	17,840	15,552
General and administrative	8,920	7,698	25,809	19,633
Total operating expenses	48,178	31,822	125,645	91,464
Loss from operations	(13,205)	(7,167)	(29,352)	(25,225)
Other income (expense)
Interest income	281		749	4
Interest expense	(6)	(1,294)	(13)	(3,138)
Change in fair value of the common stock warrant liability			(3,490)	300
Other income (expense), net	275	(1,294)	(2,754)	(2,834)
Loss before income taxes	(12,930)	(8,461)	(32,106)	(28,059)
Provision for (benefit from) income taxes	162	(1,842)	110	(4,564)
Net loss	$ (13,092)	$ (6,619)	$ (32,216)	$ (23,495)
Net loss per share, basic and diluted	$ (0.25)	$ (0.16)	$ (0.62)	$ (0.58)
Weighted average common shares outstanding, basic and diluted	52,592	40,824	51,910	40,746

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (13,092)	$ (6,619)	$ (32,216)	$ (23,495)
Other comprehensive income
Net change in unrealized gain on marketable securities, net of tax of $0 for the quarters and nine months ended September 30, 2017 and 2016	41		9
Other comprehensive income	41		9
Comprehensive loss	$ (13,051)	$ (6,619)	$ (32,207)	$ (23,495)

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (UNAUDITED) (PARENTHETICAL) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net change in unrealized gain on marketable securities, tax	$ 0	$ 0	$ 0	$ 0

CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Adjustment for change in accounting policy for stock option forfeitures			$ 72		$ (72)
Adjusted Balance	$ 291,410	$ 513	378,344	$ (41)	(87,406)
Beginning Balance at Dec. 31, 2016	291,410	$ 513	378,272	(41)	(87,334)
Beginning Balance, shares at Dec. 31, 2016		51,278,000
Net exercise of stock warrants	14,870	$ 4	14,866
Net exercise of stock warrants, shares		428,000
Stock option exercises	8,672	$ 11	8,661
Stock option exercises. shares		1,137,000
Stock-based compensation	13,044		13,044
Other comprehensive income	9			9
Net loss	(32,216)				(32,216)
Ending Balance at Sep. 30, 2017	$ 295,789	$ 528	$ 414,915	$ (32)	$ (119,622)
Ending Balance, shares at Sep. 30, 2017		52,843,000

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (32,216)	$ (23,495)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	14,786	12,690
Accretion of debt discount and accrual of paid-in-kind interest		2,083
Change in fair value of common stock warrant liability	3,490	(300)
Change in fair value of contingent consideration	367	278
Stock-based compensation	12,951	4,534
(Accretion) amortization of purchase discounts/premiums on marketable securities, net	100
Deferred income taxes	(269)	(4,820)
Provision for doubtful accounts receivable	602
Changes in operating assets and liabilities, net of effects of the acquisition:
Accounts receivable	(3,541)	(9,933)
Deferred sales commissions	(1,279)	(983)
Prepaid expenses and other current assets	(180)	(936)
Other assets	(408)	(150)
Accounts payable	(4,185)	3,250
Accrued expenses and other current liabilities	59	1,886
Deferred revenue	13,525	17,535
Other long-term liabilities	(128)	(590)
Net cash provided by operating activities	3,674	1,049
Cash flows from investing activities
Acquisition, net of cash acquired		(31,488)
Purchases of marketable securities	(51,647)
Proceeds from maturities of marketable securities	49,561
Capitalized software development costs	(3,345)	(2,326)
Purchases of property and equipment	(3,729)	(1,308)
Net cash used in investing activities	(9,160)	(35,122)
Cash flows from financing activities
Proceeds from term loan, net of issuance costs		34,469
Principal payments on capital lease obligations	(549)	(124)
Proceeds from issuance of common stock		3,075
Proceeds from exercises of stock options	8,672	2,196
Payments of initial public offering costs	(110)	(1,162)
Net cash provided by financing activities	8,013	38,454
Net increase in cash and cash equivalents	2,527	4,381
Cash and cash equivalents, beginning of period	22,118	15,205
Cash and cash equivalents, end of period	24,645	19,586
Non-cash financing and investing activities
Stock-based compensation capitalized for software development	93	70
Net exercise of stock warrants	14,870
Capitalized software development costs included in accounts payable and accrued expenses and other current liabilities at end of period	151	107
Purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities at end of period	$ 42	149
Deferred offering costs included in accounts payable and accrued expenses and other current liabilities at end of period		2,186
Term loan issuance costs included in accounts payable and accrued expenses and other current liabilities at end of period		$ 143

Company Overview	9 Months Ended
Company Overview	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Overview	Note 1 – Company overview BlackLine, Inc. and its subsidiaries (the “Company” or “BlackLine”) provide financial accounting close solutions delivered primarily as Software as a Service (“SaaS”). The Company’s solutions enable its customers to address various aspects of their financial close process including account reconciliations, variance analysis of account balances, journal entry capabilities, and certain types of data matching capabilities. The Company is headquartered in Los Angeles, California and has offices in Chicago, Atlanta, New York, Vancouver, London, Paris, Frankfurt, Sydney, Melbourne, Kuala Lumpur, Netherlands, Poland, Singapore, and South Africa.

Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements	Note 2 – Basis of presentation, significant accounting policies and recently-issued accounting pronouncements The accompanying condensed consolidated financial statements were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information. Certain information and disclosures normally included in consolidated financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the related notes included in the Annual Report on Form 10-K for the fiscal year ended December 31, 2016 filed with the Securities and Exchange Commission (“SEC”) on March 10, 2017. The condensed consolidated financial statements are unaudited and have been prepared on a basis consistent with that used to prepare the audited annual consolidated financial statements and include, in the opinion of management, all adjustments, consisting of normal and recurring items, necessary for the fair statement of the condensed consolidated financial statements. The condensed consolidated balance sheet as of December 31, 2016 was derived from audited financial statements, but does not include all disclosures required by GAAP. The operating results for the quarter and nine months ended September 30, 2017 are not necessarily indicative of the results expected for the full year ending December 31, 2017. Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the dates of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual amounts could differ from those estimates. Significant Accounting Policies There have been no material changes in the accounting policies from those disclosed in the audited consolidated financial statements and the related notes included in the Annual Report on Form 10-K. During the nine months ended September 30, 2017, the Company adopted the new stock compensation guidance and changed its policy to account for forfeitures when they occur and record income tax benefits related to stock awards in the statement of operations, subject to the need for a deferred tax asset valuation allowance – See Recently Issued Accounting Pronouncements. Recently-issued accounting standards In May 2014, the Financial Accounting Standards Board (“FASB”) issued guidance related to revenue from contracts with customers. Under this guidance, revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. The updated standard will replace all existing revenue recognition guidance under GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. In July 2015, the FASB voted to defer the effective date to January 1, 2018, with early adoption beginning January 1, 2017. In March, April, May, and December 2016, the FASB issued amendments to the new guidance relating to reporting revenue on a gross versus net basis, identifying performance obligations and licensing arrangements and other narrow scope improvements. The Company will adopt the new revenue guidance in the first quarter of 2018 using the full retrospective method to restate each prior reporting period presented. While the Company is currently assessing the impact of the new revenue guidance on its arrangements, we anticipate this standard will have a material impact on our consolidated financial statements. The Company currently believes that the new guidance will impact the amount and timing of incremental costs of obtaining a contract, such as sales commissions. The Company generally does not pay sales commissions upon contract renewal. Accordingly, under the new revenue guidance, the sales commissions will be recognized over an estimated period of benefit rather than over the non-cancelable term under current guidance. The new guidance is also expected to impact the Company’s on-premise solutions subject to current software revenue recognition guidance, as the Company may be required to recognize as revenue a significant portion of the contract consideration upon delivery of the software compared to the current practice of recognizing the contract consideration ratably over time for certain arrangements. The new guidance will also require incremental disclosures of the Company’s revenue arrangements. The Company is in process of quantifying the impact of these changes. Adoption of this standard will also require changes to the Company’s business processes, systems and controls to support the new revenue recognition guidance. The Company is in the process of identifying and implementing such changes. In February 2016, the FASB issued new guidance which significantly changes the accounting for leases. The new guidance requires a lessee recognize in the balance sheet a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. If a lessee makes this election, it should recognize lease expense for such leases generally on a straight-line basis over the lease term. For income statement purposes, the new guidance retained a dual model, requiring leases to be classified as either operating or financing. Operating leases will result in straight-line expense while finance leases will result in a front-loaded expense pattern similar to existing capital lease guidance. For statement of cash flow purposes, the new guidance also retained the existing dual method, where cash payments for operating leases are reflected in cash flows from operating activities and principal and interest payments for finance leases are reflected in cash flows from financing activities and cash flows from operating activities, respectively. The new guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The new guidance requires the recognition and measurement of leases at the beginning of the earliest period presented using a modified retrospective approach. The use of the modified retrospective approach allows an entity to use a number of practical expedients in the application of this new guidance. Although the Company is evaluating the impact of adopting this guidance on its consolidated financial statements, the Company expects that most of its operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance. In March 2016, the FASB issued new guidance to simplify various aspects relating to accounting for stock-based compensation and related tax impacts, the classification of excess tax benefits on the statement of cash flows, statutory tax withholding requirements, and other stock-based compensation classification matters. The guidance was effective for annual reporting periods beginning after December 15, 2016 and interim periods within those annual periods. The Company adopted this guidance during the first quarter ended March 31, 2017. Upon adoption, the Company changed an accounting policy to account for forfeitures when they occur rather than estimate a forfeiture rate. The impact of this change in policy increased the Company’s accumulated deficit and additional paid-in capital by $0.1 million as of January 1, 2017. The new guidance also requires the Company to record, on a prospective basis, the income tax effects of stock-based compensation awards in the income statement as discrete items, subject to deferred tax asset valuation allowance considerations, in the reporting period in which they occur, which will increase volatility in the Company’s income tax provision in the future to the extent that the Company is able to realize the tax benefits. In addition, upon adoption previously unrecognized tax benefits were recorded as an adjustment to accumulated deficit, subject to assessment for the need for a deferred tax asset valuation allowance, as of January 1, 2017. The Company had $36.7 million of net operating losses related to tax benefits for stock-based compensation awards as of December 31, 2016 which were not recorded as deferred tax assets. As the Company has a full valuation allowance against its deferred tax assets, the adoption of this guidance did not have a material impact on the Company’s financial statements. In June 2016, the FASB issued guidance which requires that financial assets measured at amortized costs be presented at the net amount expected to be collected. This guidance amends the accounting for credit losses for available-for-sale securities and purchased financial assets with credit deterioration. This guidance is effective for annual periods beginning after December 15, 2019, and interim periods within those annual periods. Early adoption is permitted for any interim or annual period after December 15, 2018. The Company has not determined the impact of this guidance on its consolidated financial statements. In November 2016, the FASB issued guidance which requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning and ending total amounts shown on the statement of cash flows. This guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those years, and should be applied using a retrospective transition method to each period presented. Early adoption is permitted, including adoption in an interim period. If an entity early adopts the amendments in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. The Company’s restricted cash as of September 30, 2017 and December 31, 2016 was $0.4 million and therefore, the adoption of this guidance is not expected to have a material impact on the Company’s consolidated statements of cash flows. In February 2017, the FASB issued guidance which simplifies the subsequent measurement of goodwill by no longer requiring an entity to determine goodwill impairment by calculating the implied fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities as if that reporting unit had been acquired in a business combination. Under this new guidance, an entity would perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and would recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized would not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity would consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. Under the new guidance, an entity continues to have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. This guidance is effective for fiscal years beginning after December 15, 2019 and interim periods within those years. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The adoption of this guidance is not expected to have a material impact on the Company’s consolidated financial statements. In March 2017, the FASB issued guidance which shortens the amortization period for certain purchased callable debt securities held at a premium. Under this new guidance, an entity would shorten the amortization period of the premium to the earliest call date. This guidance is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, including adoption in an interim period. The Company has not determined the impact of this guidance on its consolidated financial statements. In May 2017, the FASB issued guidance to clarify which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. Under this guidance an entity should account for the effects of a modification unless all the following are met: 1) The fair value of the modified award is the same as the fair value of the original award immediately before the original award is modified. If the modification does not affect any of the inputs to the valuation technique that the entity uses to value the award, the entity is not required to estimate the value immediately before and after the modification; 2) The vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before the original award is modified; and 3) The classification of the modified award as an equity instrument or a liability instrument is the same as the classification of the original award immediately before the original award is modified. The amendments in this guidance are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017 and should be applied prospectively to an award modified on or after the adoption date. Early adoption is permitted, including adoption in any interim period. The Company is assessing the impact of this guidance but does not regularly or frequently modify the terms of equity awards so the adoption of this guidance is not expected to have a material impact on the Company’s consolidated financial statements. In July 2017, the FASB issued guidance which changes the classification analysis of certain equity-linked financial instruments or embedded features, for example warrants and convertible debt, with down round features. When determining whether certain financial instruments should be classified as liabilities or equity instruments, a down round feature no longer precludes equity classification when assessing whether the instrument is indexed to an entity’s own stock. The amendments also clarify existing disclosure requirements for equity-classified instruments. As a result, a freestanding equity-linked financial instrument or embedded conversion option no longer would be accounted for as a derivative liability at fair value as a result of the existence of a down round feature. This new guidance also amends existing earnings per share guidance to recognize the effect of the down round feature when it is triggered. This guidance is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, including adoption in an interim period. If the guidance is adopted in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. This new guidance may be adopted on a modified retrospective approach by means of a cumulative-effect adjustment to the statement of financial position as of the beginning of the first fiscal year and interim period in which the guidance is effective or on a full retrospective basis. The Company’s warrants to purchase common stock which were exercised in May 2017 were liability classified and recorded at fair value each period as a result of down round features. The Company is assessing the impact of this guidance and its adoption method.

Investments in Marketable Securities

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Investments in Marketable Securities

Note 3 – Investments in Marketable Securities

Investments in marketable securities presented within current assets on the consolidated balance sheet consisted of the following:

	September 30, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Marketable securities
U.S. treasury securities	$	21,473	$	1	$	(19	)	$	21,455
Corporate bonds		28,627		—		(12	)		28,615
Commercial paper		27,257		—		—			27,257
Asset-backed securities		7,800		—		(2	)		7,798
	$	85,157	$	1	$	(33	)	$	85,125

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Marketable securities
U.S. treasury securities	$	29,742	$	—	$	(17	)	$	29,725
Corporate bonds		25,522		—		(21	)		25,501
Commercial paper		15,554		—		—			15,554
Asset-backed securities		12,353		—		(3	)		12,350
	$	83,171	$	—	$	(41	)	$	83,130

Gross realized gains and losses on marketable securities and net gains and losses reclassified from accumulated other comprehensive loss to earnings were not material for the quarter and nine months ended September 30, 2017.

As of September 30, 2017, the Company’s marketable securities have a contractual maturity within one year.

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2017

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Note 4 – Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2017		2016
Accrued salaries and employee benefits	$	10,612	$	11,589
Accrued commissions to third-party partners		2,726		2,081
Accrued income and other taxes payable		878		1,553
Accrued professional services costs		563		454
Short-term portion of capital lease		442		992
Short-term tenant improvement allowance		341		341
Accrued initial public offering costs		—		110
Other accrued expenses and current liabilities		2,792		1,811
	$	18,354	$	18,931

Fair Value Measurements

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

Note 5 – Fair value measurements

The following table summarizes the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy. Financial assets and financial liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement (in thousands):

	September 30, 2017
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	15,983	$	—	$	—	$	15,983
Marketable securities
U.S. treasury securities		21,455		—		—		21,455
Corporate bonds		—		28,615		—		28,615
Commercial paper		—		27,257		—		27,257
Asset-backed securities		—		7,798		—		7,798
Total assets	$	37,438	$	63,670	$	—	$	101,108
Liabilities
Contingent consideration		—		—		5,605		5,605
Total liabilities	$	—	$	—	$	5,605	$	5,605


	December 31, 2016
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	18,936	$	—	$	—	$	18,936
Marketable securities
U.S. treasury securities		29,725		—		—		29,725
Corporate bonds		—		25,501		—		25,501
Commercial paper		—		15,554		—		15,554
Asset-backed securities		—		12,349		—		12,349
Total assets	$	48,661	$	53,404	$	—	$	102,065
Liabilities
Common stock warrant liability	$	—	$	—	$	11,380	$	11,380
Contingent consideration		—		—		5,238		5,238
Total liabilities	$	—	$	—	$	16,618	$	16,618

The following table summarizes the changes in the common stock warrant liability (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017			2016
Beginning fair value	$	—	$	5,200	$	11,380		$	5,500
Change in fair value		—		—		3,490			(300	)
Exercise of stock warrants		—		—		(14,870	)		—
Ending fair value	$	—	$	5,200	$	—		$	5,200

In May 2017, warrants to purchase 499,999 shares of common stock were net exercised resulting in the issuance of 428,033 shares of common stock and, accordingly, there we be no future changes in the fair value.

The following table summarizes the changes in the contingent consideration liability (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Beginning fair value	$	5,427	$	5,010	$	5,238	$	4,867
Change in fair value		178		135		367		278
Ending fair value	$	5,605	$	5,145	$	5,605	$	5,145

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Commitment and Contingencies	9 Months Ended
Commitment and Contingencies	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	Note 6 – Commitments and contingencies Operating Leases - The Company has various non-cancelable operating leases for its corporate and international offices. These leases expire at various times through 2024. Certain lease agreements contain renewal options, rent abatement, and escalation clauses and entitle the Company to receive a tenant allowance from the landlord. The Company records tenant allowances as a deferred rent credit, which the Company amortizes on a straight-line basis, as a reduction of rent expense, over the term of the underlying lease. Contingent Consideration - On September 3, 2013, BlackLine Systems, Inc. was acquired by BlackLine, Inc. (the “2013 Acquisition”). In conjunction with the 2013 Acquisition, option holders of BlackLine Systems, Inc. were allowed to cancel their stock option rights and receive a cash payment equal to the amount of calculated gain (less applicable expense and other items) had they exercised their stock options and then sold their common shares as part of the 2013 Acquisition. As a condition of the 2013 Acquisition, the Company is required to pay additional cash consideration to certain equity holders if the Company realizes a tax benefit from the use of net operating losses generated from the stock option exercises concurrent with the 2013 Acquisition. The maximum contingent cash consideration to be distributed is $8.0 million. The fair value of the contingent consideration was $5.6 million and $5.2 million as of September 30, 2017 and December 31, 2016, respectively. Litigation - From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. The Company is not currently a party to any legal proceedings, nor is it aware of any pending or threatened litigation, that would have a material adverse effect on the Company’s business, results of operations, cash flows or financial condition should such litigation be resolved unfavorably. Indemnification - In the ordinary course of business, the Company may provide indemnification of varying scope and terms to customers, vendors, investors, directors and officers with respect to certain matters, including, but not limited to, losses arising out of our breach of such agreements, services to be provided by the Company, or from intellectual property infringement claims made by third parties. These indemnification provisions may survive termination of the underlying agreement and the maximum potential amount of future payments the Company could be required to make under these indemnification provisions may not be subject to maximum loss clauses. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is indeterminable. The Company has never paid a material claim, nor has it been sued in connection with these indemnification arrangements. As of September 30, 2017 and December 31, 2016, the Company has not accrued a liability for these indemnification arrangements because the likelihood of incurring a payment obligation, if any, in connection with these indemnification arrangements is not probable or reasonably estimable.

Stock Based Compensation Plans

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation Plans

Note 7 – Stock-based compensation plans

Stock-based compensation

The following table summarizes the stock-based compensation that has been included in the following line items within the unaudited condensed consolidated statements of operations (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of revenues	$	334	$	150	$	855	$	425
Sales and marketing		7,761		501		9,169		1,834
Research and development		236		198		534		532
General and administrative		784		511		2,393		1,743
	$	9,115	$	1,360	$	12,951	$	4,534

On July 21, 2017, the Company modified the vesting terms of options for certain Australian employees to purchase 219,000 shares of common stock to a time-based vesting schedule. Prior to the modification, the options vested solely upon a change in control of the Company. The Company recorded $5.8 million of stock-based compensation in the quarter ended September 30, 2017 relating to this modification. In addition, the Company recorded an additional $1.1 million relating to the modification of an award in connection with the termination of an employee.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Note 8 – Income taxes In determining quarterly provisions for income taxes, the Company uses the annual estimated effective tax rate applied to the actual year-to-date loss, adjusted for discrete items arising in that quarter. The Company’s annual estimated effective tax rate differs from the U.S. federal statutory rate of 34% primarily as a result of state taxes, foreign taxes, and changes in the Company’s valuation allowance for domestic income taxes. For the quarter ended September 30, 2017 and 2016, the Company recorded $0.2 million in income tax expense related to foreign taxes and $1.8 million in income tax benefit, respectively. For the nine months ended September 30, 2017 and 2016, the Company recorded $0.1 million in income tax expense related to foreign taxes and $4.6 million in income tax benefit, respectively. The income tax benefit for the 2016 period was a result of the amortization of deferred tax liabilities recorded as a result of the 2013 Acquisition.

Net Loss Per Share

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

Note 9 – Net loss per share

Basic and diluted loss per share is calculated by dividing net loss by the weighted average number of shares of common stock outstanding. As the Company has net losses for the periods presented all potentially dilutive common stock, which are comprised of stock options and warrants, are antidilutive.

The following potentially dilutive shares have been excluded from the calculation of diluted net loss per share attributable to common stockholders because they are antidilutive (in thousands):

	September 30,
	2017		2016
Options to purchase common stock		5,604		5,247
Common stock warrants		—		500
Total shares excluded from net loss per share		5,604		5,747

Business Combinations

9 Months Ended

Sep. 30, 2017

Business Combinations [Abstract]

Business Combinations

Note 10 - Business combinations

On August 31, 2016, the Company acquired Runbook Company B.V., a Netherlands-based provider of licensed financial close automation software and integration for SAP customers, or Runbook, which the Company refers to as the “Runbook Acquisition.” The primary purpose of the Runbook Acquisition was to enhance our position as a leading provider of software solutions to automate the financial close process for SAP customers and secondarily it supports our European expansion strategy.

The following table presents the Company’s unaudited pro forma information, as if the acquisition occurred on January 1, 2015 (in thousands):

	Quarter Ended			Nine Months Ended
	September 30, 2016			September 30, 2016
Pro forma total revenues	$	33,808		$	92,856
Pro forma net loss	$	(5,535	)	$	(23,391	)
Pro forma net loss per share, basic and diluted	$	(0.14	)	$	(0.57	)

The pro forma results reflect certain adjustments for the depreciation and amortization of the fair value of the intangible assets acquired and related tax adjustments. Such pro forma amounts are not necessarily indicative of the results that actually would have occurred had the acquisition been completed on the date indicated, nor is it indicative of the future operating results of the Company.

Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the dates of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual amounts could differ from those estimates.
Recently-Issued Accounting Standards	Recently-issued accounting standards In May 2014, the Financial Accounting Standards Board (“FASB”) issued guidance related to revenue from contracts with customers. Under this guidance, revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. The updated standard will replace all existing revenue recognition guidance under GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. In July 2015, the FASB voted to defer the effective date to January 1, 2018, with early adoption beginning January 1, 2017. In March, April, May, and December 2016, the FASB issued amendments to the new guidance relating to reporting revenue on a gross versus net basis, identifying performance obligations and licensing arrangements and other narrow scope improvements. The Company will adopt the new revenue guidance in the first quarter of 2018 using the full retrospective method to restate each prior reporting period presented. While the Company is currently assessing the impact of the new revenue guidance on its arrangements, we anticipate this standard will have a material impact on our consolidated financial statements. The Company currently believes that the new guidance will impact the amount and timing of incremental costs of obtaining a contract, such as sales commissions. The Company generally does not pay sales commissions upon contract renewal. Accordingly, under the new revenue guidance, the sales commissions will be recognized over an estimated period of benefit rather than over the non-cancelable term under current guidance. The new guidance is also expected to impact the Company’s on-premise solutions subject to current software revenue recognition guidance, as the Company may be required to recognize as revenue a significant portion of the contract consideration upon delivery of the software compared to the current practice of recognizing the contract consideration ratably over time for certain arrangements. The new guidance will also require incremental disclosures of the Company’s revenue arrangements. The Company is in process of quantifying the impact of these changes. Adoption of this standard will also require changes to the Company’s business processes, systems and controls to support the new revenue recognition guidance. The Company is in the process of identifying and implementing such changes. In February 2016, the FASB issued new guidance which significantly changes the accounting for leases. The new guidance requires a lessee recognize in the balance sheet a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. If a lessee makes this election, it should recognize lease expense for such leases generally on a straight-line basis over the lease term. For income statement purposes, the new guidance retained a dual model, requiring leases to be classified as either operating or financing. Operating leases will result in straight-line expense while finance leases will result in a front-loaded expense pattern similar to existing capital lease guidance. For statement of cash flow purposes, the new guidance also retained the existing dual method, where cash payments for operating leases are reflected in cash flows from operating activities and principal and interest payments for finance leases are reflected in cash flows from financing activities and cash flows from operating activities, respectively. The new guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The new guidance requires the recognition and measurement of leases at the beginning of the earliest period presented using a modified retrospective approach. The use of the modified retrospective approach allows an entity to use a number of practical expedients in the application of this new guidance. Although the Company is evaluating the impact of adopting this guidance on its consolidated financial statements, the Company expects that most of its operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance. In March 2016, the FASB issued new guidance to simplify various aspects relating to accounting for stock-based compensation and related tax impacts, the classification of excess tax benefits on the statement of cash flows, statutory tax withholding requirements, and other stock-based compensation classification matters. The guidance was effective for annual reporting periods beginning after December 15, 2016 and interim periods within those annual periods. The Company adopted this guidance during the first quarter ended March 31, 2017. Upon adoption, the Company changed an accounting policy to account for forfeitures when they occur rather than estimate a forfeiture rate. The impact of this change in policy increased the Company’s accumulated deficit and additional paid-in capital by $0.1 million as of January 1, 2017. The new guidance also requires the Company to record, on a prospective basis, the income tax effects of stock-based compensation awards in the income statement as discrete items, subject to deferred tax asset valuation allowance considerations, in the reporting period in which they occur, which will increase volatility in the Company’s income tax provision in the future to the extent that the Company is able to realize the tax benefits. In addition, upon adoption previously unrecognized tax benefits were recorded as an adjustment to accumulated deficit, subject to assessment for the need for a deferred tax asset valuation allowance, as of January 1, 2017. The Company had $36.7 million of net operating losses related to tax benefits for stock-based compensation awards as of December 31, 2016 which were not recorded as deferred tax assets. As the Company has a full valuation allowance against its deferred tax assets, the adoption of this guidance did not have a material impact on the Company’s financial statements. In June 2016, the FASB issued guidance which requires that financial assets measured at amortized costs be presented at the net amount expected to be collected. This guidance amends the accounting for credit losses for available-for-sale securities and purchased financial assets with credit deterioration. This guidance is effective for annual periods beginning after December 15, 2019, and interim periods within those annual periods. Early adoption is permitted for any interim or annual period after December 15, 2018. The Company has not determined the impact of this guidance on its consolidated financial statements. In November 2016, the FASB issued guidance which requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning and ending total amounts shown on the statement of cash flows. This guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those years, and should be applied using a retrospective transition method to each period presented. Early adoption is permitted, including adoption in an interim period. If an entity early adopts the amendments in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. The Company’s restricted cash as of September 30, 2017 and December 31, 2016 was $0.4 million and therefore, the adoption of this guidance is not expected to have a material impact on the Company’s consolidated statements of cash flows. In February 2017, the FASB issued guidance which simplifies the subsequent measurement of goodwill by no longer requiring an entity to determine goodwill impairment by calculating the implied fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities as if that reporting unit had been acquired in a business combination. Under this new guidance, an entity would perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and would recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized would not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity would consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. Under the new guidance, an entity continues to have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. This guidance is effective for fiscal years beginning after December 15, 2019 and interim periods within those years. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The adoption of this guidance is not expected to have a material impact on the Company’s consolidated financial statements. In March 2017, the FASB issued guidance which shortens the amortization period for certain purchased callable debt securities held at a premium. Under this new guidance, an entity would shorten the amortization period of the premium to the earliest call date. This guidance is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, including adoption in an interim period. The Company has not determined the impact of this guidance on its consolidated financial statements. In May 2017, the FASB issued guidance to clarify which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. Under this guidance an entity should account for the effects of a modification unless all the following are met: 1) The fair value of the modified award is the same as the fair value of the original award immediately before the original award is modified. If the modification does not affect any of the inputs to the valuation technique that the entity uses to value the award, the entity is not required to estimate the value immediately before and after the modification; 2) The vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before the original award is modified; and 3) The classification of the modified award as an equity instrument or a liability instrument is the same as the classification of the original award immediately before the original award is modified. The amendments in this guidance are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017 and should be applied prospectively to an award modified on or after the adoption date. Early adoption is permitted, including adoption in any interim period. The Company is assessing the impact of this guidance but does not regularly or frequently modify the terms of equity awards so the adoption of this guidance is not expected to have a material impact on the Company’s consolidated financial statements. In July 2017, the FASB issued guidance which changes the classification analysis of certain equity-linked financial instruments or embedded features, for example warrants and convertible debt, with down round features. When determining whether certain financial instruments should be classified as liabilities or equity instruments, a down round feature no longer precludes equity classification when assessing whether the instrument is indexed to an entity’s own stock. The amendments also clarify existing disclosure requirements for equity-classified instruments. As a result, a freestanding equity-linked financial instrument or embedded conversion option no longer would be accounted for as a derivative liability at fair value as a result of the existence of a down round feature. This new guidance also amends existing earnings per share guidance to recognize the effect of the down round feature when it is triggered. This guidance is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, including adoption in an interim period. If the guidance is adopted in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. This new guidance may be adopted on a modified retrospective approach by means of a cumulative-effect adjustment to the statement of financial position as of the beginning of the first fiscal year and interim period in which the guidance is effective or on a full retrospective basis. The Company’s warrants to purchase common stock which were exercised in May 2017 were liability classified and recorded at fair value each period as a result of down round features. The Company is assessing the impact of this guidance and its adoption method.

Investments in Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Schedule of Investments in Marketable Securities

Investments in marketable securities presented within current assets on the consolidated balance sheet consisted of the following:

	September 30, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Marketable securities
U.S. treasury securities	$	21,473	$	1	$	(19	)	$	21,455
Corporate bonds		28,627		—		(12	)		28,615
Commercial paper		27,257		—		—			27,257
Asset-backed securities		7,800		—		(2	)		7,798
	$	85,157	$	1	$	(33	)	$	85,125

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Marketable securities
U.S. treasury securities	$	29,742	$	—	$	(17	)	$	29,725
Corporate bonds		25,522		—		(21	)		25,501
Commercial paper		15,554		—		—			15,554
Asset-backed securities		12,353		—		(3	)		12,350
	$	83,171	$	—	$	(41	)	$	83,130

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2017		2016
Accrued salaries and employee benefits	$	10,612	$	11,589
Accrued commissions to third-party partners		2,726		2,081
Accrued income and other taxes payable		878		1,553
Accrued professional services costs		563		454
Short-term portion of capital lease		442		992
Short-term tenant improvement allowance		341		341
Accrued initial public offering costs		—		110
Other accrued expenses and current liabilities		2,792		1,811
	$	18,354	$	18,931

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

	September 30, 2017
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	15,983	$	—	$	—	$	15,983
Marketable securities
U.S. treasury securities		21,455		—		—		21,455
Corporate bonds		—		28,615		—		28,615
Commercial paper		—		27,257		—		27,257
Asset-backed securities		—		7,798		—		7,798
Total assets	$	37,438	$	63,670	$	—	$	101,108
Liabilities
Contingent consideration		—		—		5,605		5,605
Total liabilities	$	—	$	—	$	5,605	$	5,605


	December 31, 2016
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	18,936	$	—	$	—	$	18,936
Marketable securities
U.S. treasury securities		29,725		—		—		29,725
Corporate bonds		—		25,501		—		25,501
Commercial paper		—		15,554		—		15,554
Asset-backed securities		—		12,349		—		12,349
Total assets	$	48,661	$	53,404	$	—	$	102,065
Liabilities
Common stock warrant liability	$	—	$	—	$	11,380	$	11,380
Contingent consideration		—		—		5,238		5,238
Total liabilities	$	—	$	—	$	16,618	$	16,618

Common Stock Warrant Liability

Summary of Changes in Common Stock Warrant Liability and Contingent Consideration Liability

The following table summarizes the changes in the common stock warrant liability (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017			2016
Beginning fair value	$	—	$	5,200	$	11,380		$	5,500
Change in fair value		—		—		3,490			(300	)
Exercise of stock warrants		—		—		(14,870	)		—
Ending fair value	$	—	$	5,200	$	—		$	5,200

Contingent Consideration

Summary of Changes in Common Stock Warrant Liability and Contingent Consideration Liability

The following table summarizes the changes in the contingent consideration liability (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Beginning fair value	$	5,427	$	5,010	$	5,238	$	4,867
Change in fair value		178		135		367		278
Ending fair value	$	5,605	$	5,145	$	5,605	$	5,145

Stock Based Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation

The following table summarizes the stock-based compensation that has been included in the following line items within the unaudited condensed consolidated statements of operations (in thousands):

	Quarter Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of revenues	$	334	$	150	$	855	$	425
Sales and marketing		7,761		501		9,169		1,834
Research and development		236		198		534		532
General and administrative		784		511		2,393		1,743
	$	9,115	$	1,360	$	12,951	$	4,534

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share Attributable to Common Stockholders

The following potentially dilutive shares have been excluded from the calculation of diluted net loss per share attributable to common stockholders because they are antidilutive (in thousands):

	September 30,
	2017		2016
Options to purchase common stock		5,604		5,247
Common stock warrants		—		500
Total shares excluded from net loss per share		5,604		5,747

Business Combinations (Tables)

9 Months Ended

Sep. 30, 2017

Business Combinations [Abstract]

Schedule of Unaudited Pro Forma Information

The following table presents the Company’s unaudited pro forma information, as if the acquisition occurred on January 1, 2015 (in thousands):

	Quarter Ended			Nine Months Ended
	September 30, 2016			September 30, 2016
Pro forma total revenues	$	33,808		$	92,856
Pro forma net loss	$	(5,535	)	$	(23,391	)
Pro forma net loss per share, basic and diluted	$	(0.14	)	$	(0.57	)

Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2017	Jan. 01, 2017
Accumulated Deficit
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Adjustment for change in accounting policy for stock option forfeitures			$ (0.1)
Additional Paid-in Capital
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Adjustment for change in accounting policy for stock option forfeitures			$ 0.1
New Accounting Pronouncement, Early Adoption, Effect
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Net operating losses related to tax benefits for stock-based compensation awards	$ 36.7
Restricted cash	$ 0.4	$ 0.4

Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 85,157	$ 83,171
Gross Unrealized Gains	1
Gross Unrealized Losses	(33)	(41)
Fair Value	85,125	83,130
U.S. treasury securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,473	29,742
Gross Unrealized Gains	1
Gross Unrealized Losses	(19)	(17)
Fair Value	21,455	29,725
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	28,627	25,522
Gross Unrealized Losses	(12)	(21)
Fair Value	28,615	25,501
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	27,257	15,554
Fair Value	27,257	15,554
Asset-backed securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,800	12,353
Gross Unrealized Losses	(2)	(3)
Fair Value	$ 7,798	$ 12,350

Investments in Marketable Securities - Additional Information (Details)	9 Months Ended
	Sep. 30, 2017
Maximum
Schedule Of Available For Sale Securities [Line Items]
Marketable securities contractual maturity period	1 year

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued salaries and employee benefits	$ 10,612	$ 11,589
Accrued commissions to third-party partners	2,726	2,081
Accrued income and other taxes payable	878	1,553
Accrued professional services costs	563	454
Short-term portion of capital lease	442	992
Short-term tenant improvement allowance	341	341
Accrued initial public offering costs		110
Other accrued expenses and current liabilities	2,792	1,811
Accrued expenses and other current liabilities	$ 18,354	$ 18,931

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 101,108	$ 102,065
Liabilities
Common stock warrant liability		11,380
Contingent consideration	5,605	5,238
Total liabilities	5,605	16,618
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	15,983	18,936
U.S. treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	21,455	29,725
Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	28,615	25,501
Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	27,257	15,554
Asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	7,798	12,349
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	37,438	48,661
Level 1 \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	15,983	18,936
Level 1 \| U.S. treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	21,455	29,725
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	63,670	53,404
Level 2 \| Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	28,615	25,501
Level 2 \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	27,257	15,554
Level 2 \| Asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	7,798	12,349
Level 3
Liabilities
Common stock warrant liability		11,380
Contingent consideration	5,605	5,238
Total liabilities	$ 5,605	$ 16,618

Fair Value Measurements - Summary of Changes in Common Stock Warrant Liability (Details) - Common Stock Warrant Liability - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Beginning fair value	$ 5,200	$ 11,380	$ 5,500
Change in fair value		3,490	(300)
Exercise of stock warrants		$ (14,870)
Ending fair value	$ 5,200		$ 5,200

Fair Value Measurements - Additional Information (Details) - Common Stock - shares	1 Months Ended	9 Months Ended
	May 31, 2017	Sep. 30, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase of common stock	499,999
Issuance of common stock	428,033	428,000

Fair Value Measurements - Summary of Changes in Contingent Consideration Liability (Details) - Contingent Consideration - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Beginning fair value	$ 5,427	$ 5,010	$ 5,238	$ 4,867
Change in fair value	178	135	367	278
Ending fair value	$ 5,605	$ 5,145	$ 5,605	$ 5,145

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions		9 Months Ended
	Sep. 03, 2013	Sep. 30, 2017	Dec. 31, 2016
Business Acquisition Contingent Consideration [Line Items]
Lease expiration year		2024
BlackLine Systems, Inc.
Business Acquisition Contingent Consideration [Line Items]
Maximum contingent cash consideration to be distributed	$ 8.0
BlackLine Systems, Inc. \| Contingent Consideration
Business Acquisition Contingent Consideration [Line Items]
Fair value of contingent consideration		$ 5.6	$ 5.2

Stock Based Compensation Plans - Summary of Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9,115	$ 1,360	$ 12,951	$ 4,534
Cost of Revenues
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	334	150	855	425
Sales and Marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	7,761	501	9,169	1,834
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	236	198	534	532
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 784	$ 511	$ 2,393	$ 1,743

Stock Based Compensation Plans - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Jul. 21, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation		$ 5,800	$ 12,951	$ 4,534
Australia
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock options granted to purchase shares of common stock for employee	219,000
Termination of an Employee
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Additional stock-based compensation relating to the modification of an award	$ 1,100

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
U.S. Federal statutory rate			34.00%
Income tax expense (benefit)	$ 162	$ (1,842)	$ 110	$ (4,564)

Net Loss Per Share - Schedule of Potentially Dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from net loss per share	5,604	5,747
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from net loss per share	5,604	5,247
Common stock warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from net loss per share		500

Business Combinations - Schedule of Unaudited Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016
Business Combinations [Abstract]
Pro forma total revenues	$ 33,808	$ 92,856
Pro forma net loss	$ (5,535)	$ (23,391)
Pro forma net loss per share, basic and diluted	$ (0.14)	$ (0.57)