Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, value at Dec. 31, 2010	$ 706,878	$ 576,905	$ 117,692	$ 12,281
Balance, shares at Dec. 31, 2010		39,338
Net Income	14,411		14,411
Other comprehensive income	8,404			8,404
Issuance of common stock - stock option and other plans, value	410	410
Issuance of common stock - stock option and other plans, shares		25
Issuance of common stock - restricted stock awards, net of cancelled awards, value	763	763
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		114
Repurchase and retirement of common stock, shares		(2)
SRepurchase and retirement of common stock, value	(32)	(32)
Cash dividends paid on common stock	(3,154)		(3,154)
Balance, value at Jun. 30, 2011	727,680	578,046	128,949	20,685
Balance, shares at Jun. 30, 2011		39,475
Balance, value at Dec. 31, 2011	759,338	579,136	155,069	25,133
Balance, shares at Dec. 31, 2011		39,506
Net Income	20,801		20,801
Other comprehensive income	702			702
Issuance of common stock - stock option and other plans, value	314	314
Issuance of common stock - stock option and other plans, shares		19
Issuance of common stock - restricted stock awards, net of cancelled awards, value	908	908
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		130
Cash dividends paid on common stock	(23,351)		(23,351)
Balance, value at Jun. 30, 2012	$ 758,712	$ 580,358	$ 152,519	$ 25,835
Balance, shares at Jun. 30, 2012		39,655