Transactions - Secondary Offering (Details) - $ / shares shares in Millions		1 Months Ended
	Jun. 05, 2015	Mar. 31, 2017	Sep. 30, 2016	Mar. 30, 2017	Dec. 31, 2016	Sep. 19, 2016	Sep. 18, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015
Business Acquisition [Line Items]
Share price (in usd per share)								$ 10.33	$ 14.73	$ 19.51
Class A | Common Stock
Business Acquisition [Line Items]
Issuance of common stock (in shares)	13.2	7.5	8.6
Share price (in usd per share)	$ 17.00	$ 19.53	$ 22.50
Class A | Common Stock | Investor Stockholders
Business Acquisition [Line Items]
Issuance of common stock (in shares)		4.4	2.2
Class A | Common Stock | Evolent Health, Selling Stockholders
Business Acquisition [Line Items]
Issuance of common stock (in shares)		3.1	6.4
Evolent Health LLC
Business Acquisition [Line Items]
Parent's ownership percentage	70.30%	83.90%		77.40%	77.40%	74.60%	71.00%