Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Regular Dividend	Special Dividend	Common Stock	Common Stock Special Dividend	Additional Paid-in Capital	Additional Paid-in Capital Special Dividend	(Accumulated Deficit) Retained Earnings	(Accumulated Deficit) Retained Earnings Regular Dividend	(Accumulated Deficit) Retained Earnings Special Dividend
BALANCE (in shares) at Dec. 31, 2012				100,105
BALANCE at Dec. 31, 2012	$ 1,521,620			$ 1,001		$ 1,146,488		$ 374,131
Net income	300,835							300,835
Issuance of common stock (in shares)				20
Issuance of common stock	27					27
Retirement of common stock (in shares)				(180)
Retirement of common stock	(6,693)			$ (2)		(6,691)
Dividend on common stock (in shares)					13,878
Dividend on common stock		$ (221,196)	$ (135,546)		$ 139		$ 542,541		$ (221,196)	$ (678,226)
Restricted stock compensation, net of forfeitures (in shares)				(30)
Restricted stock compensation, net of forfeitures	9,822					9,381		441
Stock option compensation expense, net of forfeitures	3,116					3,116
Income tax benefit of equity compensation	351					351
Restricted stock grant (in shares)				300
Restricted stock grant				$ 3		(3)
Stock options exercised (in shares)				1,830
Stock options exercised	30,171			$ 18		30,153
BALANCE (in shares) at Dec. 31, 2013				115,923
BALANCE at Dec. 31, 2013	1,502,507			$ 1,159		1,725,363		(224,015)
Net income	195,022							195,022
Retirement of common stock (in shares)				(118)
Retirement of common stock	(4,036)			$ (1)		(4,035)
Dividend on common stock		(239,086)							(239,086)
Restricted stock compensation, net of forfeitures (in shares)				(20)
Restricted stock compensation, net of forfeitures	12,093					11,985		108
Stock option compensation expense, net of forfeitures	1,882					1,882
Income tax benefit of equity compensation	665					665
Restricted stock grant (in shares)				267
Restricted stock grant	3			$ 3
Stock options exercised (in shares)				712
Stock options exercised	12,450			$ 7		12,443
BALANCE (in shares) at Dec. 31, 2014				116,764
BALANCE at Dec. 31, 2014	1,481,500			$ 1,168		1,748,303		(267,971)
Net income	221,854							221,854
Retirement of common stock (in shares)				(237)
Retirement of common stock	(9,454)			$ (3)		(9,451)
Dividend on common stock		$ (254,774)							$ (254,774)
Restricted stock compensation, net of forfeitures (in shares)				(11)
Restricted stock compensation, net of forfeitures	14,712					14,639		73
Stock option compensation expense, net of forfeitures	682					682
Income tax benefit of equity compensation	525					525
Restricted stock grant (in shares)				303
Restricted stock grant	3			$ 3
Stock options exercised (in shares)				413
Stock options exercised	7,700			$ 4		7,696
BALANCE (in shares) at Dec. 31, 2015				117,232
BALANCE at Dec. 31, 2015	$ 1,462,748			$ 1,172		$ 1,762,394		$ (300,818)