Earnings (Loss) Per Common Share - Computation of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Income (loss) from continuing operations		$ (13,040)	$ (37,035)	$ (33,337)	$ (317,535)
Income (loss) from discontinued operations, net of tax	[1]	0	(1,135)	1,383	(2,908)
Net income (loss)		(13,040)	(38,170)	(31,954)	(320,443)
Less:
Net loss attributable to non-controlling interests		0	(822)	0	(822)
Net loss attributable to common shareholders of Evolent Health, Inc.		(13,040)	(37,348)	(31,954)	(319,621)
Net loss attributable to common shareholders of Evolent Health, Inc.		$ (13,040)	$ (37,348)	$ (31,954)	$ (319,621)
Weighted-average common shares outstanding - basic (in shares)		85,800	85,172	85,306	82,615
Weighted-average common shares outstanding - diluted (in shares)		85,800	85,172	85,306	82,615
Loss per common share, Basic and diluted
Continuing operations, basic (in dollars per share)		$ (0.15)	$ (0.43)	$ (0.39)	$ (3.84)
Continuing operations, diluted (in dollars per share)		(0.15)	(0.43)	(0.39)	(3.84)
Discontinued operations, diluted (in dollars per share)		0	(0.01)	0.02	(0.03)
Discontinued operations, basic (in dollars per share)		0	(0.01)	0.02	(0.03)
Diluted loss per share attributable to common shareholders of Evolent Health, Inc. (in dollars per share)		(0.15)	(0.44)	(0.37)	(3.87)
Basic loss per share attributable to common shareholders of Evolent Health, Inc. (in dollars per share)		$ (0.15)	$ (0.44)	$ (0.37)	$ (3.87)

[1] Includes $1.9 million gain on disposal of discontinued operations for the nine months ended September 30, 2021