Earnings (Loss) Per Common Share - Computation of Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Net loss	$ (199,293)	$ (25,738)	$ (31,900)	$ (48,649)	$ (17,540)	$ (12,555)	$ (10,031)	$ (14,065)	$ (305,580)	$ (54,191)	$ (69,767)
Less:
Net loss attributable to non-controlling interests	(1,197)	(217)	(285)	(1,910)	(853)	(126)	(115)	(439)	(3,609)	(1,533)	(9,102)
Net loss attributable to common shareholders of Evolent Health, Inc.	$ (198,096)	$ (25,521)	$ (31,615)	$ (46,739)	$ (16,687)	$ (12,429)	$ (9,916)	$ (13,626)	$ (301,971)	$ (52,658)	$ (60,665)
Weighted-average common shares outstanding - Basic and diluted (in shares)									82,364,000	77,338,000	64,351,000
Loss per common share
Basic and diluted (in dollars per share)	$ (2.36)	$ (0.30)	$ (0.38)	$ (0.59)	$ (0.21)	$ (0.16)	$ (0.13)	$ (0.18)	$ (3.67)	$ (0.68)	$ (0.94)
Class B Common Stock
Loss per common share
Convertible preferred stock, shares issued upon conversion (in shares)	1								1