Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands	Total	COMMON STOCK	CAPITAL SURPLUS	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE INCOME
Balance at beginning of period at Dec. 31, 2010		$ 15,369	$ 73,040	$ 361,680	$ 8,505
Shares issued		37	722
Shares acquired and canceled		(280)		(9,772)
Tax effect of stock options			187
Stock-based compensation arrangements			1,017
Net income	34,023			34,023
Dividends on common stock				(11,791)
Net change	1,659				1,659
Balance at end of period at Sep. 30, 2011	474,396	15,126	74,966	374,140	10,164
Balance at beginning of period at Jun. 30, 2011		15,273	74,229	371,150	9,745
Shares issued		16	248
Shares acquired and canceled		(163)		(5,466)
Tax effect of stock options			118
Stock-based compensation arrangements			371
Net income	12,553			12,553
Dividends on common stock				(4,097)
Net change	419				419
Balance at end of period at Sep. 30, 2011	474,396	15,126	74,966	374,140	10,164
Balance at beginning of period at Dec. 31, 2011	483,041	15,118	77,462	381,017	9,444
Shares issued		89	1,470
Shares acquired and canceled		(7)		(249)
Tax effect of stock options			629
Stock-based compensation arrangements			1,189
Net income	39,594			39,594
Dividends on common stock				(12,630)
Net change	(2,739)				(2,739)
Balance at end of period at Sep. 30, 2012	510,387	15,200	80,750	407,732	6,705
Balance at beginning of period at Jun. 30, 2012		15,154	79,181	398,267	6,959
Shares issued		46	748
Tax effect of stock options			430
Stock-based compensation arrangements			391
Net income	13,860			13,860
Dividends on common stock				(4,395)
Net change	(254)				(254)
Balance at end of period at Sep. 30, 2012	$ 510,387	$ 15,200	$ 80,750	$ 407,732	$ 6,705