General – Impact of Adoption of ASC 606 on Consolidated Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating results by business segment
Net revenue	$ 1,853,506	$ 1,419,406	$ 5,469,506	$ 4,144,168
Cost of goods sold	571,145	543,682	1,689,229	1,648,670
Total costs and expenses	1,812,545	1,374,431	5,398,793	4,059,330
Income before income taxes	40,961	44,975	70,713	84,838
Provision for income taxes	13,816	11,739	18,565	29,206
Net income	27,145	33,236	52,148	55,632
Net income attributable to Magellan	27,145	32,451	52,148	55,698
Managed care and other
Operating results by business segment
Net revenue	1,235,787	834,358	3,670,890	2,385,397
PBM
Operating results by business segment
Net revenue	617,719	$ 585,048	1,798,616	$ 1,758,771
ASU 2014-09 | Adjustments
Operating results by business segment
Net revenue	(5,302)		(1,058)
Cost of goods sold	651		651
Total costs and expenses	651		651
Income before income taxes	(5,953)		(1,709)
Provision for income taxes	(1,566)		(449)
Net income	(4,387)		(1,260)
Net income attributable to Magellan	(4,387)		(1,260)
ASU 2014-09 | Adjustments | Managed care and other
Operating results by business segment
Net revenue	(1,588)		(5,543)
ASU 2014-09 | Adjustments | PBM
Operating results by business segment
Net revenue	(3,714)		4,485
ASU 2014-09 | Balance Without ASC 606 Adoption
Operating results by business segment
Net revenue	1,848,204		5,468,448
Cost of goods sold	571,796		1,689,880
Total costs and expenses	1,813,196		5,399,444
Income before income taxes	35,008		69,004
Provision for income taxes	12,250		18,116
Net income	22,758		50,888
Net income attributable to Magellan	22,758		50,888
ASU 2014-09 | Balance Without ASC 606 Adoption | Managed care and other
Operating results by business segment
Net revenue	1,234,199		3,665,347
ASU 2014-09 | Balance Without ASC 606 Adoption | PBM
Operating results by business segment
Net revenue	$ 614,005		$ 1,803,101