Transactions - New Mexico Health Connections (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 02, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Identifiable intangible assets acquired and liabilities assumed
Goodwill		$ 768,124	$ 628,186	$ 626,569
Provider network contracts
Identifiable intangible assets acquired and liabilities assumed
Useful life		5 years
New Mexico Health Connections
Business Acquisition [Line Items]
Transaction costs			$ 1,200
Purchase consideration:
Payments to acquire businesses	$ 10,000
Contingent consideration, liability	252
Consideration transferred	10,252
Identifiable intangible assets acquired and liabilities assumed
Accrued compensation and employee benefits	(474)
Goodwill	5,826
Net assets acquired	10,252
New Mexico Health Connections | Customer relationships
Identifiable intangible assets acquired and liabilities assumed
Identifiable intangible assets	$ 2,700
Useful life	15 years
New Mexico Health Connections | Provider network contracts
Identifiable intangible assets acquired and liabilities assumed
Identifiable intangible assets	$ 2,300
Useful life	5 years
New Mexico Health Connections | Above market lease
Identifiable intangible assets acquired and liabilities assumed
Identifiable intangible assets	$ (100)