General – Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Operating results by business segment
Net revenue	$ 1,853,506	$ 5,469,506
Transferred at a point in time
Operating results by business segment
Net revenue	617,719	1,798,616
Transferred over time
Operating results by business segment
Net revenue	1,235,787	3,670,890
PBM, including dispensing
Operating results by business segment
Net revenue	501,493	1,477,321
Medicare Part D
Operating results by business segment
Net revenue	116,226	321,295
PBA
Operating results by business segment
Net revenue	33,158	99,792
Formulary management
Operating results by business segment
Net revenue	16,601	55,326
Other service lines
Operating results by business segment
Net revenue	598	2,320
Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue	377,533	1,128,547
Behavioral & Specialty Health | EAP risk-based
Operating results by business segment
Net revenue	79,854	265,787
Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	74,399	213,961
Magellan Complete Care | Risk-based, non-EAP
Operating results by business segment
Net revenue	639,584	1,863,771
Magellan Complete Care | ASO
Operating results by business segment
Net revenue	14,060	41,386
Government
Operating results by business segment
Net revenue	1,112,310	3,281,697
Non-government
Operating results by business segment
Net revenue	741,196	2,187,809
Healthcare
Operating results by business segment
Net revenue	1,176,439	3,488,928
Healthcare | Transferred over time
Operating results by business segment
Net revenue	1,176,439	3,488,928
Healthcare | Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue	377,615	1,128,743
Healthcare | Behavioral & Specialty Health | EAP risk-based
Operating results by business segment
Net revenue	79,854	265,787
Healthcare | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	65,326	189,241
Healthcare | Magellan Complete Care | Risk-based, non-EAP
Operating results by business segment
Net revenue	639,584	1,863,771
Healthcare | Magellan Complete Care | ASO
Operating results by business segment
Net revenue	14,060	41,386
Healthcare | Government
Operating results by business segment
Net revenue	874,135	2,585,525
Healthcare | Non-government
Operating results by business segment
Net revenue	302,304	903,403
Pharmacy Management
Operating results by business segment
Net revenue	725,234	2,123,136
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	665,734	1,940,726
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	59,500	182,410
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	549,508	1,619,431
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	116,226	321,295
Pharmacy Management | PBA
Operating results by business segment
Net revenue	33,158	99,792
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue	16,601	55,326
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue	598	2,320
Pharmacy Management | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	9,143	24,972
Pharmacy Management | Government
Operating results by business segment
Net revenue	238,175	696,172
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	487,059	1,426,964
Elimination
Operating results by business segment
Net revenue	(48,167)	(142,558)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue	(48,015)	(142,110)
Elimination | Transferred over time
Operating results by business segment
Net revenue	(152)	(448)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue	(48,015)	(142,110)
Elimination | Behavioral & Specialty Health | Risk-based, non-EAP
Operating results by business segment
Net revenue	(82)	(196)
Elimination | Behavioral & Specialty Health | ASO
Operating results by business segment
Net revenue	(70)	(252)
Elimination | Non-government
Operating results by business segment
Net revenue	$ (48,167)	$ (142,558)