General - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating results by business segment
Net revenue	$ 1,100,075	$ 1,154,289	$ 2,222,454	$ 2,273,295
Transferred at a point in time
Operating results by business segment
Net revenue	551,364	545,675	1,120,575	1,098,133
Transferred over time
Operating results by business segment
Net revenue	548,711	608,614	1,101,879	1,175,162
Government
Operating results by business segment
Net revenue	431,382	409,818	862,441	868,928
Non-government
Operating results by business segment
Net revenue	668,693	744,471	1,360,013	1,404,367
Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	344,107	400,526	693,862	762,256
Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	77,419	87,296	157,357	176,913
Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	71,589	68,471	142,163	131,920
PBM, including dispensing
Operating results by business segment
Net revenue	494,653	475,832	1,008,198	964,949
Medicare Part D
Operating results by business segment
Net revenue	56,711	69,843	112,377	133,184
PBA
Operating results by business segment
Net revenue	30,811	33,476	60,940	67,453
Formulary management
Operating results by business segment
Net revenue	25,061	18,426	47,222	35,609
Other service lines
Operating results by business segment
Net revenue	(276)	419	335	1,011
Healthcare
Operating results by business segment
Net revenue	481,021	546,113	969,927	1,052,935
Healthcare | Transferred over time
Operating results by business segment
Net revenue	481,021	546,113	969,927	1,052,935
Healthcare | Government
Operating results by business segment
Net revenue	222,393	236,014	449,495	467,076
Healthcare | Non-government
Operating results by business segment
Net revenue	258,628	310,099	520,432	585,859
Healthcare | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	344,199	400,591	694,044	762,399
Healthcare | Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	77,419	87,296	157,357	176,913
Healthcare | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	59,403	58,226	118,526	113,623
Pharmacy Management
Operating results by business segment
Net revenue	624,062	612,658	1,262,275	1,229,118
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	556,195	550,010	1,129,973	1,106,575
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	67,867	62,648	132,302	122,543
Pharmacy Management | Government
Operating results by business segment
Net revenue	208,989	173,804	412,946	401,852
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	415,073	438,854	849,329	827,266
Pharmacy Management | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	12,271	10,327	23,805	18,470
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	499,484	480,167	1,017,596	973,391
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	56,711	69,843	112,377	133,184
Pharmacy Management | PBA
Operating results by business segment
Net revenue	30,811	33,476	60,940	67,453
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue	25,061	18,426	47,222	35,609
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue	(276)	419	335	1,011
Elimination
Operating results by business segment
Net revenue	(5,008)	(4,482)	(9,748)	(8,758)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue	(4,831)	(4,335)	(9,398)	(8,442)
Elimination | Transferred over time
Operating results by business segment
Net revenue	(177)	(147)	(350)	(316)
Elimination | Non-government
Operating results by business segment
Net revenue	(5,008)	(4,482)	(9,748)	(8,758)
Elimination | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	(92)	(65)	(182)	(143)
Elimination | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	(85)	(82)	(168)	(173)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue	$ (4,831)	$ (4,335)	$ (9,398)	$ (8,442)