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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 13,613	$ 13,551	$ 14,044	$ 25,003
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	24,101	24,569	24,024	24,460
Common stock equivalents-stock options (in shares)	153	669	132	738
Common stock equivalents-RSAs (in shares)	7	33	7	28
Common stock equivalents-RSUs (in shares)	18	23	19	50
Common stock equivalents- PSUs( in shares)	130	111	127	232
Common stock equivalents-employee stock purchase plan (in shares)	7	2	6	2
Weighted average number of common shares outstanding-diluted (in shares)	24,416	25,407	24,315	25,510
Net income per common share-basic (in dollars per share)	$ 0.56	$ 0.55	$ 0.58	$ 1.02
Net income per common share-diluted (in dollars per share)	$ 0.56	$ 0.53	$ 0.58	$ 0.98
Potential dilutive securities excluded from computation of dilutive securities (in shares)	1,100	500	1,100	300