General - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating results by business segment
Net revenue	$ 1,161,649	$ 1,122,379
Transferred at a point in time
Operating results by business segment
Net revenue	535,573	569,211
Transferred over time
Operating results by business segment
Net revenue	626,076	553,168
Government
Operating results by business segment
Net revenue	412,330	431,059
Non-government
Operating results by business segment
Net revenue	749,319	691,320
Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	373,356	349,755
Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	88,120	79,938
Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	83,190	70,574
PBM, including dispensing
Operating results by business segment
Net revenue	535,397	513,545
Medicare Part D
Operating results by business segment
Net revenue	176	55,666
PBA
Operating results by business segment
Net revenue	49,882	30,129
Formulary management
Operating results by business segment
Net revenue		22,161
Formulary management | Government
Operating results by business segment
Net revenue	29,183
Other service lines
Operating results by business segment
Net revenue		611
Other service lines | Non-government
Operating results by business segment
Net revenue	2,345
Healthcare
Operating results by business segment
Net revenue	533,010	488,906
Healthcare | Transferred over time
Operating results by business segment
Net revenue	533,010	488,906
Healthcare | Government
Operating results by business segment
Net revenue	256,292	227,102
Healthcare | Non-government
Operating results by business segment
Net revenue	276,718	261,804
Healthcare | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	373,442	349,845
Healthcare | Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	88,120	79,938
Healthcare | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	71,448	59,123
Pharmacy Management
Operating results by business segment
Net revenue	632,199	638,213
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	538,972	573,778
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	93,227	64,435
Pharmacy Management | Government
Operating results by business segment
Net revenue	156,038	203,957
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	476,161	434,256
Pharmacy Management | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	11,817	11,534
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	538,796	518,112
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	176	55,666
Pharmacy Management | PBA
Operating results by business segment
Net revenue	49,882	30,129
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue		22,161
Pharmacy Management | Formulary management | Government
Operating results by business segment
Net revenue	29,183
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue		611
Pharmacy Management | Other service lines | Non-government
Operating results by business segment
Net revenue	2,345
Elimination
Operating results by business segment
Net revenue	(3,560)	(4,740)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue	(3,399)	(4,567)
Elimination | Transferred over time
Operating results by business segment
Net revenue	(161)	(173)
Elimination | Non-government
Operating results by business segment
Net revenue	(3,560)	(4,740)
Elimination | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	(86)	(90)
Elimination | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	(75)	(83)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue	$ (3,399)	$ (4,567)