Consolidated Statement of Stockholders' Equity (USD $) In Thousands	Total	Special Dividend	Regular Dividend	Common Stock	Common Stock Special Dividend	Additional Paid-in Capital	Additional Paid-in Capital Special Dividend	Retained Earnings	Retained Earnings Special Dividend	Retained Earnings Regular Dividend
Beginning Balance at Dec. 31, 2011	$ 1,480,022			$ 995		$ 1,129,435		$ 277,592
Beginning Balance (in shares) at Dec. 31, 2011				99,528
Net income	69,014							69,014
Issuance of common stock	12					12
Retirement of common stock (in shares)				(100)
Retirement of common stock	(2,481)			(1)		(2,480)
Dividend on common stock			(20,060)							(20,060)
Restricted stock compensation, net of forfeitures (in shares)				(7)
Restricted stock compensation, net of forfeitures	3,576					3,576
Income tax benefit of equity compensation	2,094					2,094
Stock option compensation expense, net of forfeitures	2,315					2,315
Restricted stock grant (in shares)				332
Restricted stock grant				3		(3)
Stock options exercised (in shares)				224
Stock options exercised	2,078			3		2,075
Ending Balance at Jun. 30, 2012	1,464,570			1,000		1,137,024		326,546
Ending Balance (in shares) at Jun. 30, 2012				99,977
Beginning Balance at Dec. 31, 2012	1,521,620			1,001		1,146,488		374,131
Beginning Balance (in shares) at Dec. 31, 2012				100,105
Net income	201,521							201,521
Issuance of common stock (in shares)				19
Issuance of common stock	13					13
Retirement of common stock (in shares)				(144)
Retirement of common stock	(5,454)			(1)		(5,453)
Dividend on common stock (in shares)					13,878
Dividend on common stock		(135,546)	(109,488)		139		542,541		(678,226)	(109,488)
Restricted stock compensation, net of forfeitures (in shares)				(12)
Restricted stock compensation, net of forfeitures	4,721					4,445		276
Income tax benefit of equity compensation	31					31
Stock option compensation expense, net of forfeitures	1,677					1,677
Restricted stock grant (in shares)				300
Restricted stock grant				3		(3)
Stock options exercised (in shares)				1,272
Stock options exercised	22,094			12		22,082
Ending Balance at Jun. 30, 2013	$ 1,501,189			$ 1,154		$ 1,711,821		$ (211,786)
Ending Balance (in shares) at Jun. 30, 2013				115,418