CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ 319,267	$ 547	$ 451,571	$ 45	$ (132,896)
Beginning Balance, shares at Dec. 31, 2018		54,683
Stock option exercises	2,762	$ 1	2,761
Stock option exercises, shares		170
Vesting of restricted stock units	2	$ 2
Vesting of restricted stock units, shares		178
Acquisition of common stock for tax withholding obligations	(1,729)		(1,729)
Stock-based compensation	6,515		6,515
Net loss attributable to BlackLine, Inc., including adjustment to redeemable non-controlling interest	(8,781)				(8,781)
Ending Balance at Mar. 31, 2019	318,036	$ 550	459,118	45	(141,677)
Ending Balance, shares at Mar. 31, 2019		55,031
Beginning Balance at Dec. 31, 2019	398,613	$ 559	561,275	377	(163,598)
Beginning Balance, shares at Dec. 31, 2019		55,931
Stock option exercises	4,654	$ 3	4,651
Stock option exercises, shares		231
Vesting of restricted stock units	2	$ 2
Vesting of restricted stock units, shares		217
Acquisition of common stock for tax withholding obligations	(3,562)		(3,562)
Stock-based compensation	9,636		9,636
Other comprehensive loss	(311)			(311)
Net loss attributable to BlackLine, Inc., including adjustment to redeemable non-controlling interest	(12,843)		(2,201)		(10,642)
Ending Balance at Mar. 31, 2020	$ 396,189	$ 564	$ 569,799	$ 66	$ (174,240)
Ending Balance, shares at Mar. 31, 2020		56,379