Net Income per Common Share Attributable to Magellan Helath, Inc (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income attributable to Magellan	$ 32,451	$ 25,509	$ 55,698	$ 42,704
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	23,282	23,052	23,135	23,394
Common stock equivalents-stock options (in shares)	572	226	485	287
Common stock equivalents-RSAs (in shares)	483	696	461	647
Common stock equivalents-RSUs (in shares)	61	29	46	28
Common stock equivalents- PSUs( in shares)	162	2	111	23
Common stock equivalents-employee stock purchase plan (in shares)	3	4	3	3
Weighted average number of common shares outstanding-diluted (in shares)	24,563	24,009	24,241	24,382
Net income attributable to Magellan per common share-basic (in dollars per share)	$ 1.39	$ 1.11	$ 2.41	$ 1.83
Net income attributable to Magellan per common share-diluted (in dollars per share)	$ 1.32	$ 1.06	$ 2.30	$ 1.75
Potential dilutive securities excluded from computation of dilutive securities (in shares)	400	1,800	600	1,200