Stockholders' Equity (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income attributable to Magellan Health Inc	$ 21,565	$ 27,133	$ 4,986	$ 25,720					$ 79,404	$ 125,261	$ 151,027
Denominator:
Weighted average number of common shares outstanding-basic	25,558,000	26,703,000	27,144,000	27,370,000	27,285,000	26,990,000	26,829,000	27,110,000	26,689,000	27,054,000	27,386,000
Common stock equivalents-stock options (in shares)									495,000	564,000	406,000
Common stock equivalents-restricted stock awards (in shares)									155,000	13,000	11,000
Common stock equivalents-restricted stock units (in shares)									14,000	42,000	77,000
Common stock equivalents-employee stock purchase plan (in shares)									2,000	2,000	2,000
Weighted average number of common shares outstanding-diluted (in shares)	26,382,000	27,242,000	27,765,000	28,051,000	28,008,000	27,704,000	27,338,000	27,648,000	27,355,000	27,675,000	27,882,000
Net income per common share-basic:	$ 0.84	$ 1.02	$ 0.18	$ 0.94	$ 0.68	$ 1.75	$ 1.17	$ 1.03	$ 2.98	$ 4.63	$ 5.51
Net income per common share-diluted:	$ 0.82	$ 1.00	$ 0.18	$ 0.92	$ 0.67	$ 1.70	$ 1.15	$ 1.01	$ 2.90	$ 4.53	$ 5.42
Potential dilutive securities excluded from computation of dilutive securities (in shares)									700,000	800,000	2,200,000