Statements of Shareholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2013	$ 769,117	$ 7	$ 515,331	$ (2,291)	$ 256,070	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	8,797		8,797
Repurchase of common stock	(1,630)			(1,630)
Proceeds from options exercised	174		174
Excess tax benefits from share-based compensation	1,871		1,871
Changes in comprehensive income	(718)					(718)
Net income	225,464				225,464
Balance at Dec. 31, 2014	1,003,075	7	526,173	(3,921)	481,534	(718)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	9,222		9,222
Repurchase of common stock	(112,261)			(112,261)
Proceeds from options exercised	32		32
Excess tax benefits from share-based compensation	8,850		8,850
Changes in comprehensive income	(828)					(828)
Net income	317,220				317,220
Balance at Dec. 31, 2015	1,225,310	7	544,277	(116,182)	798,754	(1,546)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	7,105		7,105
Repurchase of common stock	(102,510)			(102,510)
Proceeds from options exercised	92		92
Excess tax deficiency from share-based compensation	(470)		(470)
Changes in comprehensive income	201					201
Net income	264,879				264,879
Balance at Dec. 31, 2016	$ 1,394,607	$ 7	$ 551,004	$ (218,692)	$ 1,063,633	$ (1,345)