Basis of Presentation, Significant Accounting Policies and Recently-Issued Accounting Pronouncements - Schedule of Revisions for the Financial Statement - Condensed Consolidated Statement of Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net loss	$ (10,970)	$ (9,031)
Comprehensive loss	(11,281)	(8,859)
Comprehensive loss attributable to BlackLine, Inc.	$ (10,953)	(8,647)
As Previously Reported
Net loss		(8,833)
Comprehensive loss		(8,661)
Comprehensive loss attributable to BlackLine, Inc.		(8,449)
Adjustments
Net loss		(198)
Comprehensive loss		(198)
Comprehensive loss attributable to BlackLine, Inc.		$ (198)