Net Income per Common Share Attributable to Magellan Health, Inc. - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net (loss) income from continuing operations	$ (114)	$ (17,296)	$ 21,932	$ 28,742
Accretion of redeemable non-controlling interest	(5,033)		(5,033)
Net (loss) income from continuing operations after accretion of redeemable non-controlling interest	(5,147)	(17,296)	16,899	28,742
Income from discontinued operations, net of tax	6,050	28,943	11,165	84,660
Net income after accretion of redeemable non-controlling interest, basic	903	11,647	28,064	113,402
Net income after accretion of redeemable non-controlling interest, diluted	$ 903	$ 11,647	$ 28,064	$ 113,402
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	26,247	25,448	26,120	25,078
Weighted average number of common shares outstanding-diluted (in shares)	26,247	25,448	26,626	25,317
Net (loss) income per common share-basic:
Continuing operations (in dollars per share)	$ (0.20)	$ (0.68)	$ 0.65	$ 1.15
Discontinued operations (in dollars per share)	0.23	1.14	0.43	3.37
Consolidated operations (in dollars per share)	0.03	0.46	1.08	4.52
Net (loss) income per common share-diluted:
Continuing operations (in dollars per share)	(0.20)	(0.68)	0.63	1.14
Discontinued operations (in dollars per share)	0.23	1.14	0.42	3.34
Consolidated operations (in dollars per share)	$ 0.03	$ 0.46	$ 1.05	$ 4.48
Stock Options
Denominator:
Common stock equivalents (in shares)			157	67
Restricted Stock Awards
Denominator:
Common stock equivalents (in shares)			24	22
Restricted Stock Units (RSUs)
Denominator:
Common stock equivalents (in shares)			174	76
Performance Based Restricted Stock Units ("PSUs")
Denominator:
Common stock equivalents (in shares)			150	70
Employee Stock
Denominator:
Common stock equivalents (in shares)			1	4