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	33,283		33,283
Other comprehensive income	13,406			13,406
Issuance of common stock - stock option and other plans, value	792	792
Issuance of common stock - stock option and other plans, shares		47
Issuance of common stock - restricted stock awards, net of cancelled awards, value	1,163	1,163
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		119
Repurchase and retirement of common stock, shares		(2)
SRepurchase and retirement of common stock, value	(32)	(32)
Cash dividends paid on common stock	(5,524)		(5,524)
Balance, value at Sep. 30, 2011	749,966	578,828	145,451	25,687
Balance, shares at Sep. 30, 2011		39,502
Balance, value at Dec. 31, 2011	759,338	579,136	155,069	25,133
Balance, shares at Dec. 31, 2011		39,506
Net Income	32,681		32,681
Other comprehensive income	3,345			3,345
Issuance of common stock - stock option and other plans, value	713	713
Issuance of common stock - stock option and other plans, shares		40
Issuance of common stock - restricted stock awards, net of cancelled awards, value	1,152	1,152
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		143
Cash dividends paid on common stock	(35,252)		(35,252)
Balance, value at Sep. 30, 2012	$ 761,977	$ 581,001	$ 152,498	$ 28,478
Balance, shares at Sep. 30, 2012		39,689