Net Income per Common Share Attributable to Magellan Health, Inc (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income attributable to Magellan	$ 13,551	$ 5,500	$ 25,003	$ 23,247
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	24,569	23,108	24,460	23,060
Common stock equivalents-stock options (in shares)	669	399	738	436
Common stock equivalents-RSAs (in shares)	33	439	28	421
Common stock equivalents-RSUs (in shares)	23	30	50	56
Common stock equivalents- PSUs( in shares)	111	61	232	62
Common stock equivalents-employee stock purchase plan (in shares)	2	1	2	2
Weighted average number of common shares outstanding-diluted (in shares)	25,407	24,038	25,510	24,037
Net income per common share-basic (in dollars per share)	$ 0.55	$ 0.24	$ 1.02	$ 1.01
Net income per common share-diluted (in dollars per share)	$ 0.53	$ 0.23	$ 0.98	$ 0.97
Potential dilutive securities excluded from computation of dilutive securities (in shares)	500	800	300	700