Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements - Schedule of Revisions for the Financial Statement - Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Provision for income taxes	$ 357	$ 403
Net loss	(10,970)	(9,031)
Net loss attributable to BlackLine, Inc.	$ (12,843)	(8,781)
As Previously Reported
Provision for income taxes		205
Net loss		(8,833)
Net loss attributable to BlackLine, Inc.		(8,583)
Adjustments
Provision for income taxes		198
Net loss		(198)
Net loss attributable to BlackLine, Inc.		$ (198)