General – Impact of Adoption of ASC 606 on Consolidated Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating results by business segment
Net revenue	$ 1,810,923	$ 1,419,139	$ 3,616,000	$ 2,724,762
Income before income taxes	18,375	10,588	29,752	39,863
Provision for income taxes	4,824	5,661	4,749	17,467
Net income	13,551	4,927	25,003	22,396
Net income attributable to Magellan	13,551	5,500	25,003	23,247
Managed care and other
Operating results by business segment
Net revenue	1,215,340	821,699	2,435,103	1,551,039
PBM
Operating results by business segment
Net revenue	595,583	$ 597,440	1,180,897	$ 1,173,723
ASU 2014-09 | Adjustments
Operating results by business segment
Net revenue	546		4,244
Income before income taxes	546		4,244
Provision for income taxes	143		1,112
Net income	403		3,132
Net income attributable to Magellan	403		3,132
ASU 2014-09 | Adjustments | Managed care and other
Operating results by business segment
Net revenue	(1,203)		(3,955)
ASU 2014-09 | Adjustments | PBM
Operating results by business segment
Net revenue	1,749		8,199
ASU 2014-09 | Balance Without ASC 606 Adoption
Operating results by business segment
Net revenue	1,811,469		3,620,244
Income before income taxes	18,921		33,996
Provision for income taxes	4,967		5,861
Net income	13,954		28,135
Net income attributable to Magellan	13,954		28,135
ASU 2014-09 | Balance Without ASC 606 Adoption | Managed care and other
Operating results by business segment
Net revenue	1,214,137		2,431,148
ASU 2014-09 | Balance Without ASC 606 Adoption | PBM
Operating results by business segment
Net revenue	$ 597,332		$ 1,189,096