Consolidated Statement Of Stockholders' Equity (USD $) In Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Total
Balance as of at Dec. 31, 2010	$ 1,098	$ 1,354,691	$ 115,082	$ 1,470,871
Balance as of (shares) at Dec. 31, 2010	109,754
Net income			40,330	40,330
Issuance of common stock		12		12
Issuance of common stock, shares	1
Retirement of common stock	(19)	(46,134)		(46,153)
Retirement of common stock, shares	(1,904)
Restricted stock compensation, net of forfeitures	(1)	1,532		1,531
Restricted stock compensation, net of forfeitures, shares	(9)
Income tax benefit of equity compensation		751		751
Stock option compensation expense, net of forfeitures		1,172		1,172
Restricted stock grant	2	(2)
Restricted stock grant, shares	166
Stock options exercised	1	774		775
Stock options exercised, shares	86
Balance as of at Mar. 31, 2011	1,081	1,312,796	155,412	1,469,289
Balance as of (shares) at Mar. 31, 2011	108,094
Balance as of at Dec. 31, 2011	995	1,129,435	277,592	1,408,022
Balance as of (shares) at Dec. 31, 2011	99,528
Net income			31,680	31,680
Issuance of common stock		7		7
Issuance of common stock, shares
Retirement of common stock	(1)	(2,390)		(2,391)
Retirement of common stock, shares	(98)
Restricted stock compensation, net of forfeitures		1,576		1,576
Restricted stock compensation, net of forfeitures, shares	(7)
Income tax benefit of equity compensation		1,920		1,920
Stock option compensation expense, net of forfeitures		1,056		1,056
Restricted stock grant	3	(3)
Restricted stock grant, shares	332
Stock options exercised	2	1,699		1,701
Stock options exercised, shares	189
Balance as of at Mar. 31, 2012	$ 999	$ 1,133,300	$ 309,272	$ 1,443,571
Balance as of (shares) at Mar. 31, 2012	99,944