Consolidated Statements Of Stockholders Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income Loss [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2010	$ 1,066,124	$ 1,143	$ 1,094,713	$ 6,564	$ (33,732)	$ (2,564)
Net income	63,310			63,310
Change in other comprehensive income, net of tax	3,484				3,484
Common stock dividends	(45,114)			(45,114)
Issuance of common stock	123,377	125	124,100			(848)
Restricted stock compensation	3,371		3,371
Tax expense of stock-based compensation	(61)		(61)
Balance at Sep. 30, 2011	1,214,491	1,268	1,222,123	24,760	(30,248)	(3,412)
Balance at Dec. 31, 2011	1,210,199	1,268	1,224,572	32,925	(45,148)	(3,418)
Net income	81,455			81,455
Change in other comprehensive income, net of tax	6,176				6,176
Common stock dividends	(50,705)			(50,705)
Issuance of common stock	144,037	129	145,833	(377)		(1,548)
Restricted stock compensation	3,451		3,451
Tax expense of stock-based compensation	385		385
Balance at Sep. 30, 2012	$ 1,394,998	$ 1,397	$ 1,374,241	$ 63,298	$ (38,972)	$ (4,966)