Summary of Significant Accounting Policies - Significant Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant customers
Revenues	$ 1,263,385	$ 1,292,132	$ 1,164,345	$ 1,117,022	$ 1,268,743	$ 1,190,082	$ 1,157,607	$ 980,968	$ 4,836,884	$ 4,597,400	$ 3,760,118
Florida Contracts
Significant customers
Revenues									$ 548,700	439,500	253,700
Florida Medicaid Contract
Significant customers
Termination notice									1 day
Termination notice period without cause									30 days
Iowa Contracts
Significant customers
Revenues									$ 13,500	530,300	465,000
Pharmacy Management | Customer A | Service
Significant customers
Revenues									264,152	324,809	171,936
Pharmacy Management | Customer B | Service
Significant customers
Revenues									$ 139,273	$ 130,200	$ 123,812