Transactions - New Century Health (Details) - USD ($) $ in Thousands, shares in Millions		12 Months Ended
	Oct. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Purchase consideration:
Cash		$ 8,575	$ 130,241	$ 3,694
Liabilities assumed:
Goodwill		$ 572,064	768,124	$ 628,186
Technology
Liabilities assumed:
Useful life		5 years
Provider network contracts
Liabilities assumed:
Useful life		5 years
New Century Health
Business Acquisition [Line Items]
Equity method investment, ownership percentage	100.00%
Total merger consideration, net of cash on hand and certain closing adjustments	$ 205,100
Payments to acquire businesses, net	118,700
Contingent consideration arrangements (up to)	20,000
Contingent consideration arrangements fair value	3,200
Purchase consideration:
Cash	124,652
Fair value of Class B common stock issued	83,173
Fair value of contingent consideration	3,200
Total consideration	211,025
Tangible assets acquired:
Cash and cash equivalents	5,963
Accounts receivable	5,559
Prepaid expenses and other current assets	7,901
Property and equipment	381
Other non-current assets	148
Liabilities assumed:
Accounts payable	1,167
Accrued liabilities	1,494
Accrued compensation and employee benefits	3,966
Reserve for claims and performance-based arrangements	18,631
Deferred tax liabilities	24,041
Other long-term liabilities	6,138
Goodwill	133,110
Net assets acquired	$ 211,025
New Century Health | Class B Common Stock
Business Acquisition [Line Items]
Consideration transferred, equity interests issued and issuable, shares issued (in shares)	3.1
Contingent consideration arrangements (up to)	$ 11,400
New Century Health | Selling, general and administrative expenses
Business Acquisition [Line Items]
Transaction costs			$ 1,600
New Century Health | Customer relationships
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 72,500
Liabilities assumed:
Useful life	15 years
New Century Health | Technology
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 27,000
Liabilities assumed:
Useful life	5 years
New Century Health | Corporate trade name
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 4,300
Liabilities assumed:
Useful life	10 years
New Century Health | Provider network contracts
Identifiable intangible assets acquired:
Identifiable intangible assets	$ 9,600
Liabilities assumed:
Useful life	5 years
Former Owners of New Century Health | New Century Health
Business Acquisition [Line Items]
Contingent consideration arrangements (up to)	$ 11,400
Former Employees of New Century Health | New Century Health
Business Acquisition [Line Items]
Contingent consideration arrangements (up to)	$ 8,600