Transactions - Valence Health (Details) - USD ($) $ in Thousands, shares in Millions		3 Months Ended			9 Months Ended	12 Months Ended
	Oct. 03, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Mar. 30, 2017	Oct. 02, 2016	Sep. 19, 2016	Sep. 18, 2016	Dec. 31, 2015	Jun. 05, 2015
Purchase consideration:
Cash		$ 0	$ 11,500
Liabilities assumed:
Goodwill		627,204	626,569		$ 626,569	$ 626,569					$ 608,903
Measurement period adjustment, goodwill		$ 635	0
540 W. Madison Street, Suite 1400
Liabilities assumed:
Remaining lease payments	$ 20,800
Estimated sublease value	$ 13,500
540 W. Madison Street, Suite 1400 | Commitments
Liabilities assumed:
Discount rate	5.00%
Evolent Health LLC
Business Acquisition [Line Items]
Parent's ownership percentage		83.90%			77.40%	77.40%	77.40%		74.60%	71.00%		70.30%
Valence Health
Business Acquisition [Line Items]
Adjustment for removal of transaction costs				$ (2,700)	$ (2,700)
Percentage of voting interests acquired	100.00%
Percentage of issued and outstanding common stock	10.50%
Contingent consideration arrangements (up to)	$ 12,400
Contingent consideration arrangements fair value	2,600
Transaction costs	2,700
Purchase consideration:
Fair value of Class A common stock issued	159,614
Cash for settlement of software license	2,620
Cash	54,799
Total consideration	217,033
Tangible assets acquired:
Restricted cash	1,829
Receivables	8,587
Prepaid expenses and other current assets	3,465
Property and equipment	6,241
Other non-current assets	313
Favorable leases assumed (net of unfavorable leases)	4,323
Liabilities assumed:
Accounts payable	5,703
Accrued liabilities	3,865
Accrued compensation and employee benefits	9,200
Deferred revenue	2,662
Other long-term liabilities	2,328
Net deferred tax liabilities	13,316
Goodwill	142,349
Net assets acquired	217,033
Acquired receivables	9,100
Acquired receivables, estimated uncollectible	500
Deferred tax liabilities	13,300
Gain (loss) on disposition of assets	52,700
Measurement period adjustment, accrued liabilities	600
Measurement period adjustment, goodwill		$ 600
Accelerated compensation cost			$ (3,900)	$ 3,900		$ 3,900
Loss from lease abandonment						$ 6,500
Valence Health | Customer relationships
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 69,000
Liabilities assumed:
Useful life	20 years
Valence Health | Technology
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 18,000
Liabilities assumed:
Useful life	5 years
Valence Health | As Previously Determined
Purchase consideration:
Fair value of Class A common stock issued	$ 159,614
Cash for settlement of software license	2,620
Cash	54,799
Total consideration	217,033
Tangible assets acquired:
Restricted cash	1,829
Receivables	8,587
Prepaid expenses and other current assets	3,465
Property and equipment	6,241
Other non-current assets	313
Favorable leases assumed (net of unfavorable leases)	4,323
Liabilities assumed:
Accounts payable	5,703
Accrued liabilities	3,865
Accrued compensation and employee benefits	9,200
Deferred revenue	2,022
Other long-term liabilities	2,328
Net deferred tax liabilities	13,316
Goodwill	141,709
Net assets acquired	217,033
Valence Health | As Previously Determined | Customer relationships
Identifiable intangible assets acquired:
Identifiable intangible assets	69,000
Valence Health | As Previously Determined | Technology
Identifiable intangible assets acquired:
Identifiable intangible assets	18,000
Valence Health | Measurement Period Adjustment
Purchase consideration:
Fair value of Class A common stock issued	0
Cash for settlement of software license	0
Cash	0
Tangible assets acquired:
Restricted cash	0
Receivables	0
Prepaid expenses and other current assets	0
Property and equipment	0
Other non-current assets	0
Favorable leases assumed (net of unfavorable leases)	0
Liabilities assumed:
Accounts payable	0
Accrued liabilities	0
Accrued compensation and employee benefits	0
Deferred revenue	640
Other long-term liabilities	0
Net deferred tax liabilities	0
Goodwill	640
Valence Health | Measurement Period Adjustment | Customer relationships
Identifiable intangible assets acquired:
Identifiable intangible assets	0
Valence Health | Measurement Period Adjustment | Technology
Identifiable intangible assets acquired:
Identifiable intangible assets	0
Valence Health | Selling, general and administrative expenses
Business Acquisition [Line Items]
Transaction costs	2,600
Valence Health | Cost of revenue
Business Acquisition [Line Items]
Transaction costs	$ 100
Valence Health | Revenue
Liabilities assumed:
Measurement period adjustment, goodwill		$ 200
Valence Health | Evolent Health LLC
Business Acquisition [Line Items]
Parent's ownership percentage	77.20%							74.60%
Valence Health | Class A
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares)	7.0