General - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating results by business segment
Net revenue	$ 1,794,307	$ 1,739,489
Transferred at a point in time
Operating results by business segment
Net revenue	521,371	515,510
Transferred over time
Operating results by business segment
Net revenue	1,272,936	1,223,979
Government
Operating results by business segment
Net revenue	1,151,093	1,091,763
Non-government
Operating results by business segment
Net revenue	643,214	647,726
Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	349,490	361,730
Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	79,939	89,617
Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	70,572	63,255
Magellan Complete Care, risk-based, non-EAP
Operating results by business segment
Net revenue	703,369	642,571
Magellan Complete Care, ASO
Operating results by business segment
Net revenue	16,664	15,054
PBM, including dispensing
Operating results by business segment
Net revenue	465,705	452,169
Medicare Part D
Operating results by business segment
Net revenue	55,666	63,341
PBA
Operating results by business segment
Net revenue	30,128	33,977
Formulary management
Operating results by business segment
Net revenue	22,161	17,183
Other service lines
Operating results by business segment
Net revenue	613	592
Healthcare
Operating results by business segment
Net revenue	1,208,674	1,164,253
Healthcare | Transferred over time
Operating results by business segment
Net revenue	1,208,674	1,164,253
Healthcare | Government
Operating results by business segment
Net revenue	947,136	888,492
Healthcare | Non-government
Operating results by business segment
Net revenue	261,538	275,761
Healthcare | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	349,580	361,808
Healthcare | Behavioral & Specialty Health, EAP risk-based
Operating results by business segment
Net revenue	79,939	89,617
Healthcare | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	59,122	55,203
Healthcare | Magellan Complete Care, risk-based, non-EAP
Operating results by business segment
Net revenue	703,369	642,571
Healthcare | Magellan Complete Care, ASO
Operating results by business segment
Net revenue	16,664	15,054
Pharmacy Management
Operating results by business segment
Net revenue	638,213	616,460
Pharmacy Management | Transferred at a point in time
Operating results by business segment
Net revenue	573,778	556,565
Pharmacy Management | Transferred over time
Operating results by business segment
Net revenue	64,435	59,895
Pharmacy Management | Government
Operating results by business segment
Net revenue	203,957	203,271
Pharmacy Management | Non-government
Operating results by business segment
Net revenue	434,256	413,189
Pharmacy Management | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	11,533	8,143
Pharmacy Management | PBM, including dispensing
Operating results by business segment
Net revenue	518,112	493,224
Pharmacy Management | Medicare Part D
Operating results by business segment
Net revenue	55,666	63,341
Pharmacy Management | PBA
Operating results by business segment
Net revenue	30,128	33,977
Pharmacy Management | Formulary management
Operating results by business segment
Net revenue	22,161	17,183
Pharmacy Management | Other service lines
Operating results by business segment
Net revenue	613	592
Elimination
Operating results by business segment
Net revenue	(52,580)	(41,224)
Elimination | Transferred at a point in time
Operating results by business segment
Net revenue	(52,407)	(41,055)
Elimination | Transferred over time
Operating results by business segment
Net revenue	(173)	(169)
Elimination | Non-government
Operating results by business segment
Net revenue	(52,580)	(41,224)
Elimination | Behavioral & Specialty Health, risk-based, non-EAP
Operating results by business segment
Net revenue	(90)	(78)
Elimination | Behavioral & Specialty Health, ASO
Operating results by business segment
Net revenue	(83)	(91)
Elimination | PBM, including dispensing
Operating results by business segment
Net revenue	$ (52,407)	$ (41,055)