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, 2011	$ 759,338	$ 579,136	$ 155,069	$ 25,133
Balance, shares at Dec. 31, 2011		39,506
Net Income	8,902		8,902
Other comprehensive income	(1,672)			(1,672)
Issuance of common stock - stock option and other plans, value	308	308
Issuance of common stock - stock option and other plans, shares		18
Issuance of common stock - restricted stock awards, net of cancelled awards, value	450	450
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		146
Cash dividends paid on common stock	(14,623)		(14,623)
Balance, value at Mar. 31, 2012	752,703	579,894	149,348	23,461
Balance, shares at Mar. 31, 2012		39,670
Balance, value at Dec. 31, 2012	764,008	581,471	162,388	20,149
Balance, shares at Dec. 31, 2012		39,686
Net Income	12,176		12,176
Other comprehensive income	(3,430)			(3,430)
Issuance of common stock - stock option and other plans, value	326	326
Issuance of common stock - stock option and other plans, shares		18
Issuance of common stock - restricted stock awards, net of cancelled awards, value	551	551
Issuance of common stock - restricted stock awards, net of cancelled awards, shares		140
Cash dividends paid on common stock	(3,971)		(3,971)
Balance, value at Mar. 31, 2013	$ 769,660	$ 582,348	$ 170,593	$ 16,719
Balance, shares at Mar. 31, 2013		39,844