CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings
Beginning Balance at Dec. 31, 2009	$ 1,442,546	$ 1,160	$ 1,483,497	$ (42,111)
Beginning Balance (in shares) at Dec. 31, 2009		115,962
Net income	157,193			157,193
Issuance of common stock (in shares)		2
Issuance of common stock	47		47
Retirement of common stock (in shares)		(7,288)
Retirement of common stock	(148,952)	(73)	(148,879)
Restricted stock compensation, net of forfeitures (in shares)		(26)
Restricted stock compensation, net of forfeitures	5,508		5,508
Stock option compensation expense, net of forfeitures	4,091		4,091
Income tax benefit of equity compensation	3,837		3,837
Restricted stock grants (in shares)		293
Restricted stock grants		3	(3)
Stock options exercised (in shares)		811
Stock options exercised	6,601	8	6,593
Ending Balance at Dec. 31, 2010	1,470,871	1,098	1,354,691	115,082
Ending Balance (in shares) at Dec. 31, 2010		109,754
Net income	162,510			162,510
Issuance of common stock (in shares)		3
Issuance of common stock	51		51
Retirement of common stock (in shares)		(10,661)
Retirement of common stock	(239,725)	(107)	(239,618)
Restricted stock compensation, net of forfeitures (in shares)		(22)
Restricted stock compensation, net of forfeitures	6,123		6,123
Stock option compensation expense, net of forfeitures	4,210		4,210
Income tax benefit of equity compensation	1,845		1,845
Restricted stock grants (in shares)		186
Restricted stock grants		2	(2)
Stock options exercised (in shares)		268
Stock options exercised	2,137	2	2,135
Ending Balance at Dec. 31, 2011	1,408,022	995	1,129,435	277,592
Ending 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)
Dividends declared on common stock ($0.60 per share)	(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 grants (in shares)		333
Restricted stock grants		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