Net Income per Common Share Attributable to Magellan Health, Inc (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income attributable to Magellan	$ 11,452	$ 17,747
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	24,349	23,012
Common stock equivalents-stock options (in shares)	806	474
Common stock equivalents-RSAs (in shares)	24	402
Common stock equivalents-RSUs (in shares)	77	81
Common stock equivalents- PSUs( in shares)	353	66
Common stock equivalents-employee stock purchase plan (in shares)	3	3
Weighted average number of common shares outstanding-diluted (in shares)	25,612	24,038
Net income per common share-basic (in dollars per share)	$ 0.47	$ 0.77
Net income per common share-diluted (in dollars per share)	$ 0.45	$ 0.74
Potential dilutive securities excluded from computation of dilutive securities (in shares)	200	600