CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2012	$ 866	$ 1,939,628	$ 1,533,768	$ 474	$ 3,474,736
Balance, shares at Dec. 31, 2012	86,596,000
Increase (Decrease) in Stockholders' Equity
Dividends			(48,423)		(48,423)
Net income (loss)			564,689		564,689
Unrealized change in fair value of investments, net of tax				715	715
Issuance of restricted stock awards	$ 6	(6)
Issuance of service-based restricted stock awards, shares	579,000
Common stock reacquired and retired	$ (1)	(10,100)			(10,101)
Common stock reacquired and retired, shares	(153,000)
Restricted stock forfeited and retired	$ (2)	2
Restricted stock forfeited and retired, shares	(171,000)
Exercise of stock options	$ 3	14,491			14,494
Exercise of stock options, shares	276,000
Vesting of restricted stock units, shares	25,000
Stock-based compensation		26,098			26,098
Balance at Dec. 31, 2013	$ 872	1,970,113	2,050,034	1,189	4,022,208
Balance, shares at Dec. 31, 2013	87,152,000
Increase (Decrease) in Stockholders' Equity
Dividends			(55,664)		(55,664)
Net income (loss)			507,204		507,204
Unrealized change in fair value of investments, net of tax				(87)	(87)
Issuance of restricted stock awards	$ 4	(4)
Issuance of service-based restricted stock awards, shares	487,000
Common stock reacquired and retired	$ (1)	(13,559)			(13,560)
Common stock reacquired and retired, shares	(123,000)
Restricted stock forfeited and retired	$ (1)	1
Restricted stock forfeited and retired, shares	(135,000)
Exercise of stock options	$ 2	11,896			11,898
Exercise of stock options, shares	211,000
Stock-based compensation		28,633			28,633
Balance at Dec. 31, 2014	$ 876	1,997,080	2,501,574	1,102	4,500,632
Balance, shares at Dec. 31, 2014	87,592,000
Increase (Decrease) in Stockholders' Equity
Dividends			(59,313)		(59,313)
Net income (loss)			(2,408,948)		(2,408,948)
Unrealized change in fair value of investments, net of tax				(661)	(661)
Issuance of common stock	$ 69	729,468			729,537
Issuance of common stock, shares	6,900,000
Issuance of restricted stock awards	$ 5	(5)
Issuance of service-based restricted stock awards, shares	471,000
Common stock reacquired and retired	$ (2)	(21,238)			(21,240)
Common stock reacquired and retired, shares	(194,000)
Restricted stock forfeited and retired	$ (1)	1
Restricted stock forfeited and retired, shares	(90,000)
Exercise of stock options	$ 1	8,450			8,451
Exercise of stock options, shares	142,000
Stock-based compensation		36,232			36,232
Stock-based compensation tax benefit		12,988			12,988
Balance at Dec. 31, 2015	$ 948	$ 2,762,976	$ 33,313	$ 441	$ 2,797,678
Balance, shares at Dec. 31, 2015	94,821,000