CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Common Stock In Treasury	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2015	$ 513	$ (1,269,391)	$ 1,124,013	$ 1,211,310	$ (262)	$ 1,066,183
Balance (in shares) at Dec. 31, 2015	51,340	(26,648)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			37,422			37,422
Exercise of stock options	$ 6		24,542			24,548
Exercise of stock options (in shares)	494
Adjustment due to adoption of new accounting standards				99		99
Issuance of equity	$ 1		1,229			1,230
Issuance of equity (in shares)	159
Repurchase of stock		$ (106,806)				(106,806)
Repurchase of stock (in shares)		(1,828)
Adjustment to non-controlling interest			(923)			(923)
Net income attributable to Magellan				77,879		77,879
Other comprehensive income (loss)-other					87	87
Balance at Dec. 31, 2016	$ 520	$ (1,376,197)	1,186,283	1,289,288	(175)	1,099,719
Balance (in shares) at Dec. 31, 2016	51,993	(28,476)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			39,116			39,116
Exercise of stock options	$ 8		44,347			44,355
Exercise of stock options (in shares)	831
Issuance of equity	$ 2		361			363
Issuance of equity (in shares)	149
Repurchase of stock		$ (21,765)				(21,765)
Repurchase of stock (in shares)		(295)
Adjustment to non-controlling interest			4,704			4,704
Net income attributable to Magellan				110,207		110,207
Other comprehensive income (loss)-other					(205)	(205)
Balance at Dec. 31, 2017	$ 530	$ (1,397,962)	1,274,811	1,399,495	(380)	1,276,494
Balance (in shares) at Dec. 31, 2017	52,973	(28,771)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			29,472			29,472
Exercise of stock options	$ 4		23,060			23,064
Exercise of stock options (in shares)	409
Adjustment due to adoption of new accounting standards				(4,227)		(4,227)
Issuance of equity	$ 1		(698)			(697)
Issuance of equity (in shares)	154
Repurchase of stock		$ (63,040)				(63,040)
Repurchase of stock (in shares)		(830)
Net income attributable to Magellan				24,181		24,181
Other comprehensive income (loss)-other					56	56
Balance at Dec. 31, 2018	$ 535	$ (1,461,002)	$ 1,326,645	$ 1,419,449	$ (324)	$ 1,285,303
Balance (in shares) at Dec. 31, 2018	53,536	(29,601)