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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income attributable to Magellan Health, Inc.	$ 35,175	$ 25,509	$ 3,958	$ 13,237	$ 27,290	$ (7,808)	$ 4,643	$ 7,288	$ 77,879	$ 31,413	$ 79,404
Denominator:
Weighted average number of common shares outstanding-basic	22,556	23,052	23,516	23,631	23,582	24,892	25,684	25,319	23,181	24,865	26,689
Common stock equivalents-stock options (in shares)									289	316	495
Common stock equivalents-RSA (in shares)									593	626	155
Common stock equivalents-RSUs (in shares)									45	33	14
Common stock equivalents-PSUs (in shares)									45	35
Common stock equivalents-employee stock purchase plan (in shares)									3	2	2
Weighted average number of common shares outstanding-diluted (in shares)	23,493	24,009	24,643	24,511	24,402	24,892	26,776	26,399	24,156	25,877	27,355
Net (loss) income attributable to Magellan Health, Inc. per common share-basic (in dollars per share)	$ 1.56	$ 1.11	$ 0.17	$ 0.56	$ 1.16	$ (0.31)	$ 0.18	$ 0.29	$ 3.36	$ 1.26	$ 2.98
Net (loss) income attributable to Magellan Health, Inc. per common share-diluted (in dollars per share)	$ 1.50	$ 1.06	$ 0.16	$ 0.54	$ 1.12	$ (0.31)	$ 0.17	$ 0.28	$ 3.22	$ 1.21	$ 2.90
Potential dilutive securities excluded from computation of dilutive securities (in shares)									1,500	1,300	700