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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income from continuing operations	$ 47,108	$ 7,215	$ 46,038	$ (976)
Income from discontinued operations, net of tax	36,397	6,398	55,717	15,020
Net income	$ 83,505	$ 13,613	$ 101,755	$ 14,044
Denominator:
Weighted average number of common shares outstanding-basic	25,054	24,101	24,891	24,024
Common stock equivalents-stock options (in shares)	31	153	46	132
Common stock equivalents-RSAs (in shares)	28	7	25	7
Common stock equivalents-RSUs (in shares)	46	18	48	19
Common stock equivalents-PSUs (in shares)	118	130	59	127
Common stock equivalents-employee stock purchase plan (in shares)	1	7	5	6
Weighted average number of common shares outstanding-diluted (in shares)	25,278	24,416	25,074	24,315
Net income per common share - basic:
Continuing operations (in dollars per share)	$ 1.88	$ 0.30	$ 1.85	$ (0.04)
Discontinued operations (in dollars per share)	1.45	0.26	2.24	0.62
Consolidated operations (in dollars per share)	3.33	0.56	4.09	0.58
Net Income (Loss) Available to Common Stockholders, Operations, Diluted [Abstract]
Continuing operations (in dollars per share)	1.86	0.30	1.84	(0.04)
Discontinued operations (in dollars per share)	1.44	0.26	2.22	0.62
Consolidated operations (in dollars per share)	$ 3.30	$ 0.56	$ 4.06	$ 0.58