Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated Other Comprehensive Loss	Retained earnings
Balance at Dec. 31, 2014	$ 4,967,844	$ 3,720	$ 1,287,941	$ (385)	$ 3,676,568
Balance, shares at Dec. 31, 2014		372,005,502
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(353,668)				(353,668)
Other Comprehensive Income (Loss), Net of Tax	(2,969)			(2,969)
Stock-based compensation	51,817		51,817
Excess Tax Benefit from Share-based Compensation	13,177		13,177
Restricted stock:
Issued	15	$ 15	0
Issued, shares		1,462,534
Repurchased and canceled	(7,313)	$ (2)	(7,311)
Repurchased and canceled, shares		(172,786)
Forfeited	(3)	$ (3)
Forfeited, shares		(336,170)
Balance at Dec. 31, 2015	4,668,900	$ 3,730	1,345,624	(3,354)	3,322,900
Balance, shares at Dec. 31, 2015		372,959,080
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(399,679)				(399,679)
Other Comprehensive Income (Loss), Net of Tax	3,094			3,094
Stock-based compensation	48,084		48,084
Excess Tax Benefit from Share-based Compensation	(9,828)		(9,828)
Restricted stock:
Issued	20	$ 20	0
Issued, shares		2,064,508
Repurchased and canceled	(8,593)	$ (3)	(8,590)
Repurchased and canceled, shares		(337,981)
Forfeited	(2)	$ (2)
Forfeited, shares		(193,250)
Balance at Dec. 31, 2016	$ 4,301,996	$ 3,745	1,375,290	(260)	2,923,221
Balance, shares at Dec. 31, 2016	374,492,357	374,492,357
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 789,447				789,447
Other Comprehensive Income (Loss), Net of Tax	567			567
Stock-based compensation	45,854		45,854
Restricted stock:
Issued	16	$ 16	0
Issued, shares		1,585,870
Repurchased and canceled	(11,821)	$ (3)	(11,818)
Repurchased and canceled, shares		(259,729)
Forfeited	(6)	$ (6)
Forfeited, shares		(598,729)
Cumulative Effect on Retained Earnings, Net of Tax	5,150				5,150
Balance at Dec. 31, 2017	$ 5,131,203	$ 3,752	$ 1,409,326	$ 307	$ 3,717,818
Balance, shares at Dec. 31, 2017	375,219,769	375,219,769