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	26,433			26,433
Other comprehensive income (loss), net of tax	(8,213)				(8,213)
Cash dividends declared	(8,918)			(8,918)
Treasury stock issued for restricted awards	(86)			(296)		210
Recognition of restricted stock compensation expense	261		261
Tax expense from stock-based compensation	(47)		(47)
Balance at Jun. 30, 2013	546,852	77,993	77,672	453,258	(21,795)	(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	28,753			28,753
Other comprehensive income (loss), net of tax	6,668				6,668
Cash dividends declared	(9,810)			(9,810)
Treasury stock issued for restricted awards	(160)			(1,824)		1,664
Recognition of restricted stock compensation expense	430		430
Tax expense from stock-based compensation	0		0
Balance at Jun. 30, 2014	$ 597,187	$ 77,993	$ 78,570	$ 485,277	$ (6,026)	$ (38,627)