Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements - Schedule of Revisions for the Financial Statement - Condensed Consolidated Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net loss attributable to BlackLine, Inc.	$ (12,843)	$ (8,781)
Net loss	(10,970)	(9,031)
Deferred income taxes	13	320
Accrued expenses and other current liabilities	$ (10,014)	(6,362)
As Previously Reported
Net loss attributable to BlackLine, Inc.		(8,583)
Net loss		(8,833)
Accrued expenses and other current liabilities		(6,240)
Adjustments
Net loss attributable to BlackLine, Inc.		(198)
Net loss		(198)
Deferred income taxes		320
Accrued expenses and other current liabilities		$ (122)