Consolidated Statements of Changes in Stockholders’ Equity (Unaudited) (USD $) In Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member] Outstanding Common Shares Repurchased [Member]	Treasury Stock [Member] Shares Repurchased To Fund Options Exercised [Member]	Treasury Stock [Member] Shares Repurchased To Satisfy Tax Obligations [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance, beginning of period at Dec. 31, 2012	$ 315	$ 198,314				$ (10,257)	$ 241,856	$ 12,137
Repurchase of outstanding shares			(12,609)	(1,750)	(754)
Change in net unrealized gains (losses) on securities available for sale, net of taxes of approximately ($9,141) and $14,140 for the six months ended June 30, 2014 and 2013, respectively								(18,218)	(19,837)
Amortization of actuarial losses, net of taxes of approximately ($189) and ($270) for the six months ended June 30, 2014 and 2013, respectively								348	(348)
Amortization of prior service credits, net of taxes of approximately $13 and $10 for the six months ended June 30, 2014 and 2013, respectively								(12)	12
OTTI charges included in income, net of taxes of approximately ($220) for the six months ended June 30, 2013								283	(283)
Reclassification adjustment for gains included in net income, net of tax of approximately $1,257 for the six months ended June 30, 2013								(1,619)
Net income							16,383		16,383
Cash dividends declared and paid on common shares ($0.30 and $0.26 per common share for the six months ended June 30, 2014 and 2013, respectively)							(7,879)
Award of common shares released from Employee Benefit Trust (129,694 and 137,346 common shares for the six months ended June 30, 2014 and 2013, respectively)		1,556
Shares issued upon vesting of restricted stock unit awards		160				2,335	(99)
Issuance upon exercise of stock options		116				2,056	(69)		1,574
Stock-based compensation activity, net		(192)
Stock-based income tax benefit		324
Balance, end of period at Jun. 30, 2013	315	200,278			(20,979)		250,192	(7,081)	422,725
Balance, beginning of period at Dec. 31, 2013	315	201,902				(22,053)	263,743	(11,375)	432,532
Repurchase of outstanding shares			(2,143)	(1,290)	(1,142)
Change in net unrealized gains (losses) on securities available for sale, net of taxes of approximately ($9,141) and $14,140 for the six months ended June 30, 2014 and 2013, respectively								11,873	11,873
Amortization of actuarial losses, net of taxes of approximately ($189) and ($270) for the six months ended June 30, 2014 and 2013, respectively								161	(161)
Amortization of prior service credits, net of taxes of approximately $13 and $10 for the six months ended June 30, 2014 and 2013, respectively								(10)	10
Net income							21,981		21,981
Cash dividends declared and paid on common shares ($0.30 and $0.26 per common share for the six months ended June 30, 2014 and 2013, respectively)							(9,015)
Award of common shares released from Employee Benefit Trust (129,694 and 137,346 common shares for the six months ended June 30, 2014 and 2013, respectively)		1,975
Shares issued upon vesting of restricted stock unit awards		9				2,972	(395)
Issuance upon exercise of stock options		296				1,608	(45)		1,290
Stock-based compensation activity, net		392
Stock-based income tax benefit		748
Balance, end of period at Jun. 30, 2014	$ 315	$ 205,322			$ (22,048)		$ 276,269	$ 649	$ 460,507