Segment Reporting - Reconciliation of Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Net Income (Loss) Attributable to Evolent Health, Inc.	$ (12,429)	$ (12,588)	$ (35,971)	$ (47,506)
Interest income	968	411	2,918	813
Interest expense	(853)	(880)	(2,561)	(2,781)
(Provision) benefit for income taxes	(135)	1,714	(29)	2,009
Depreciation and amortization expenses	(10,352)	(7,717)	(29,882)	(21,236)
Income (loss) from equity method investees	(1,381)	(369)	(2,787)	(1,446)
Change in fair value of contingent consideration and indemnification asset	(100)	(100)	1,404	(300)
Other income (expense), net	(124)	15	(64)	21
Net income (loss) attributable to non-controlling interests	126	541	680	8,471
ASC 606 transition adjustments	0	0	(4,498)	0
Purchase accounting adjustments	(214)	(449)	(647)	(1,224)
Stock-based compensation expense	(4,047)	(5,708)	(12,560)	(16,172)
Severance costs	0	0	(1,489)	0
Amortization of contract cost assets	(658)	0	(1,797)	0
Transaction costs	(456)	(2,694)	(2,254)	(9,972)
Adjusted EBITDA	$ 4,797	$ 2,648	$ 17,595	$ (5,689)