Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, unless otherwise specified	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, 2012	$ 537,422	$ 77,993	$ 77,458	$ 436,039	$ (13,582)	$ (40,486)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,680			38,680
Other comprehensive income (loss), net of tax	(7,586)				(7,586)
Cash dividends declared	(13,379)			(13,379)
Treasury stock issued for restricted awards	(86)			(296)		210
Recognition of restricted stock compensation expense	424		424
Tax expense from stock-based compensation	(47)		(47)
Balance at Sep. 30, 2013	555,428	77,993	77,835	461,044	(21,168)	(40,276)
Balance at Dec. 31, 2013	571,306	77,993	78,140	468,158	(12,694)	(40,291)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	43,414			43,414
Other comprehensive income (loss), net of tax	5,522				5,522
Cash dividends declared	(14,858)			(14,858)
Treasury stock issued for restricted awards	(163)			(1,805)		1,642
Recognition of restricted stock compensation expense	676		676
Tax expense from stock-based compensation	0		0
Balance at Sep. 30, 2014	$ 605,897	$ 77,993	$ 78,816	$ 494,909	$ (7,172)	$ (38,649)