Stockholders' Equity - Calculation of Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income attributable to Magellan Health, Inc.	$ 27,290	$ (7,808)	$ 4,643	$ 7,288	$ 21,565	$ 27,133	$ 4,986	$ 25,720	$ 31,413	$ 79,404	$ 125,261
Denominator:
Weighted average number of common shares outstanding-basic	23,582	24,892	25,684	25,319	25,558	26,703	27,144	27,370	24,865	26,689	27,054
Common stock equivalents-stock options (in shares)									316	495	564
Common stock equivalents-RSA (in shares)									626	155	13
Common stock equivalents-RSUs (in shares)									33	14	42
Common stock equivalents-PSUs (in shares)									35
Common stock equivalents-employee stock purchase plan (in shares)									2	2	2
Weighted average number of common shares outstanding-diluted (in shares)	24,402	24,892	26,776	26,399	26,382	27,242	27,765	28,051	25,877	27,355	27,675
Net income attributable to Magellan Health, Inc. per common share-basic (in dollars per share)	$ 1.16	$ (0.31)	$ 0.18	$ 0.29	$ 0.84	$ 1.02	$ 0.18	$ 0.94	$ 1.26	$ 2.98	$ 4.63
Net income attributable to Magellan Health, Inc. per common share-diluted (in dollars per share)	$ 1.12	$ (0.31)	$ 0.17	$ 0.28	$ 0.82	$ 1.00	$ 0.18	$ 0.92	$ 1.21	$ 2.90	$ 4.53
Potential dilutive securities excluded from computation of dilutive securities (in shares)									1,300	700	800