CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (USD $) In Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings
Beginning Balance at Dec. 31, 2010	$ 1,470,871	$ 1,098	$ 1,354,691	$ 115,082
Beginning Balance (in shares) at Dec. 31, 2010		109,754
Net income	82,748			82,748
Issuance of common stock (in shares)		1
Issuance of common stock	25		25
Retirement of common stock (in shares)		(2,984)
Retirement of common stock	(72,467)	(30)	(72,437)
Restricted stock compensation, net of forfeitures (in shares)		(11)
Restricted stock compensation, net of forfeitures	2,997		2,997
Income tax benefit of equity compensation	1,692		1,692
Stock option compensation expense, net of forfeitures	2,209		2,209
Restricted stock grant (in shares)		185
Restricted stock grant		2	(2)
Stock options exercised (in shares)		224
Stock options exercised	1,744	2	1,742
Ending Balance at Jun. 30, 2011	1,489,819	1,072	1,290,917	197,830
Ending Balance (in shares) at Jun. 30, 2011		107,169
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	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)
Dividends declared on common stock ($0.20 per share)	(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