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
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net income (loss) from continuing operations	$ 28,509	$ (1,070)
Income from discontinued operations, net of tax	(682)	19,320
Net income	27,827	18,250
Net income available to common stockholders, basic	$ 27,827	$ 18,250
Denominator:
Weighted average number of common shares outstanding-basic (in shares)	25,948	24,728
Weighted average number of common shares outstanding-diluted (in shares)	26,553	24,869
Net income per common share - basic:
Continuing operations (in dollars per share)	$ 1.10	$ (0.04)
Discontinued operations (in dollars per share)	(0.03)	0.78
Consolidated operations (in dollars per share)	1.07	0.74
Net income per common share - diluted:
Continuing operations (in dollars per share)	1.07	(0.04)
Discontinued operations (in dollars per share)	(0.03)	0.78
Consolidated operations (in dollars per share)	$ 1.04	$ 0.74
Stock Options
Denominator:
Common stock equivalents (in shares)	186	61
Restricted Stock Awards
Denominator:
Common stock equivalents (in shares)	19	21
Restricted Stock Units (RSUs)
Denominator:
Common stock equivalents (in shares)	196	50
Performance Based Restricted Stock Units ("PSUs")
Denominator:
Common stock equivalents (in shares)	201
Employee Stock
Denominator:
Common stock equivalents (in shares)	3	9