Summary of Significant Accounting Policies - Recent Accounting Pronouncements and Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating cash flows	$ 66,699	$ 157,457	$ 189,673
Net revenues
Managed Care Revenue	2,300,000	2,700,000	2,600,000
Fee-For-Service, Fixed Fee and Cost-Plus Contracts Revenue	503,200	342,000	290,900
Rebate Revenues	85,400	88,700	43,600
PBM Revenue	1,500,000	1,200,000	575,700
Dispensing Revenue	221,800	211,600	216,000
Medicare Part D Revenues	272,800
Co-payments	31,000
Medicare Part D Receivables	117,500
ASU 2016-18 | Early adoption
Operating cash flows	$ (51,800)	$ (81,700)	$ (21,400)