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
Common stock issued		21	474
Shares acquired and canceled		(117)		(4,306)
Tax effect of stock options			69
Stock-based compensation arrangements			646
Net income	21,470			21,470
Dividends on common stock				(7,694)
Net change	1,240				1,240
Balance at end of period at Jun. 30, 2011	470,397	15,273	74,229	371,150	9,745
Balance at beginning of period at Mar. 31, 2011		15,390	73,935	369,189	8,313
Shares acquired and canceled		(117)		(4,306)
Tax effect of stock options			23
Stock-based compensation arrangements			271
Net income	10,115			10,115
Dividends on common stock				(3,848)
Net change	1,432				1,432
Balance at end of period at Jun. 30, 2011	470,397	15,273	74,229	371,150	9,745
Balance at beginning of period at Dec. 31, 2011	483,041	15,118	77,462	381,017	9,444
Common stock issued		43	722
Shares acquired and canceled		(7)		(249)
Tax effect of stock options			199
Stock-based compensation arrangements			798
Net income	25,734			25,734
Dividends on common stock				(8,235)
Net change	(2,485)				(2,485)
Balance at end of period at Jun. 30, 2012	499,561	15,154	79,181	398,267	6,959
Balance at beginning of period at Mar. 31, 2012		15,145	78,420	390,881	7,511
Common stock issued		16	267
Shares acquired and canceled		(7)		(249)
Tax effect of stock options			137
Stock-based compensation arrangements			357
Net income	11,729			11,729
Dividends on common stock				(4,094)
Net change	(552)				(552)
Balance at end of period at Jun. 30, 2012	$ 499,561	$ 15,154	$ 79,181	$ 398,267	$ 6,959