Consolidated Statements of Stockholders' Equity (USD $) 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
Beginning Balance at Dec. 31, 2011	$ 1,408,022			$ 995		$ 1,129,435		$ 277,592
Beginning Balance (in shares) at Dec. 31, 2011				99,528
Net income	156,761							156,761
Issuance of common stock (in shares)				1
Issuance of common stock	29					29
Retirement of common stock (in shares)				(110)
Retirement of common stock	(2,808)			(1)		(2,807)
Dividend on common stock		(60,222)							(60,222)
Restricted stock compensation, net of forfeitures (in shares)				(13)
Restricted stock compensation, net of forfeitures	7,635					7,635
Stock option compensation expense, net of forfeitures	4,661					4,661
Income tax benefit of equity compensation	2,609					2,609
Restricted stock grant (in shares)				333
Restricted stock grant				3		(3)
Stock options exercised (in shares)				366
Stock options exercised	4,933			4		4,929
Ending Balance at Dec. 31, 2012	1,521,620			1,001		1,146,488		374,131
Ending Balance (in shares) at Dec. 31, 2012				100,105
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
Ending Balance at Dec. 31, 2013	1,502,507			1,159		1,725,363		(224,015)
Ending Balance (in shares) at Dec. 31, 2013				115,923
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
Ending Balance at Dec. 31, 2014	$ 1,481,500			$ 1,168		$ 1,748,303		$ (267,971)
Ending Balance (in shares) at Dec. 31, 2014				116,764