Consolidated Statements Of Stockholders' Equity (USD $) In Thousands	Comprehensive Income [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2009		$ 1,138	$ 1,087,369	$ (12,833)	$ (30,633)	$ (1,739)	$ 1,043,302
Net income	51,119			51,119			51,119
Change in other comprehensive income, net of tax	7,152				7,152		7,152
Comprehensive income	58,271						58,271
Common stock dividends ($0.36/share)				(41,412)			(41,412)
Issuance of common stock		4	3,604			(778)	2,830
Restricted stock compensation			2,060				2,060
Tax expense of stock-based compensation			(205)				(205)
Balance at Sep. 30, 2010		1,142	1,092,828	(3,126)	(23,481)	(2,517)	1,064,846
Balance at Dec. 31, 2010		1,143	1,094,713	6,564	(33,732)	(2,564)	1,066,124
Net income	63,310			63,310			63,310
Change in other comprehensive income, net of tax	3,484				3,484		3,484
Comprehensive income	66,794						66,794
Common stock dividends ($0.36/share)				(45,114)			(45,114)
Issuance of common stock		125	124,100			(848)	123,377
Restricted stock compensation			3,371				3,371
Tax expense of stock-based compensation			(61)				(61)
Balance at Sep. 30, 2011		$ 1,268	$ 1,222,123	$ 24,760	$ (30,248)	$ (3,412)	$ 1,214,491