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	33,902			33,902			33,902
Change in other comprehensive income, net of tax	5,275				5,275		5,275
Comprehensive income	39,177						39,177
Common stock dividends ($0.24/share)				(27,584)			(27,584)
Issuance of common stock		3	2,671			(778)	1,896
Restricted stock compensation			1,418				1,418
Tax expense of stock-based compensation			(205)				(205)
Balance at Jun. 30, 2010		1,141	1,091,253	(6,515)	(25,358)	(2,517)	1,058,004
Balance at Dec. 31, 2010		1,143	1,094,713	6,564	(33,732)	(2,564)	1,066,124
Net income	39,537			39,537			39,537
Change in other comprehensive income, net of tax	3,016				3,016		3,016
Comprehensive income	42,553						42,553
Common stock dividends ($0.24/share)				(29,753)			(29,753)
Issuance of common stock		124	123,180			(848)	122,456
Restricted stock compensation			1,832				1,832
Tax expense of stock-based compensation			(62)				(62)
Balance at Jun. 30, 2011		$ 1,267	$ 1,219,663	$ 16,348	$ (30,716)	$ (3,412)	$ 1,203,150