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	$ 1,408,022			$ 995		$ 1,129,435		$ 277,592
Beginning Balance (in shares) at Dec. 31, 2011				99,528
Net income	111,353							111,353
Issuance of common stock	19					19
Retirement of common stock (in shares)				(100)
Retirement of common stock	(2,481)			(1)		(2,480)
Dividend on common stock			(40,138)							(40,138)
Restricted stock compensation, net of forfeitures (in shares)				(13)
Restricted stock compensation, net of forfeitures	5,604					5,604
Income tax benefit of equity compensation	2,191					2,191
Stock option compensation expense, net of forfeitures	3,493					3,493
Restricted stock grant (in shares)				332
Restricted stock grant				3		(3)
Stock options exercised (in shares)				301
Stock options exercised	4,015			3		4,012
Ending Balance at Sep. 30, 2012	1,492,078			1,000		1,142,271		348,807
Ending Balance (in shares) at Sep. 30, 2012				100,048
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	253,364							253,364
Issuance of common stock (in shares)				20
Issuance of common stock	20					20
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)	(165,309)		139		542,541		(678,226)	(165,309)
Restricted stock compensation, net of forfeitures (in shares)				(23)
Restricted stock compensation, net of forfeitures	7,307					6,974		333
Income tax benefit of equity compensation	40					40
Stock option compensation expense, net of forfeitures	2,368					2,368
Restricted stock grant (in shares)				300
Restricted stock grant				3		(3)
Stock options exercised (in shares)				1,695
Stock options exercised	28,538			16		28,522
Ending Balance at Sep. 30, 2013	$ 1,506,948			$ 1,158		$ 1,721,497		$ (215,707)
Ending Balance (in shares) at Sep. 30, 2013				115,831