Consolidated Statements of Changes in Stockholders’ Equity (Unaudited) (USD $) In Thousands	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]	Common Stock [Member]	Additional Paid-in Capital [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
Change in net unrealized gains (losses) on securities available for sale, net of taxes of approximately ($7,484) and $15,482 for the nine months ended September 30, 2014 and 2013, respectively								(19,947)	(19,947)
Amortization of actuarial losses, net of taxes of approximately ($266) and ($405) for the nine months ended September 30, 2014 and 2013, respectively								522	(522)
Amortization of prior service credits, net of taxes of approximately $18 and $15 for the nine months ended September 30, 2014 and 2013, respectively								(19)	19
OTTI charges included in income, net of taxes of approximately ($620) for the nine months ended September 30, 2013								799	(799)
Reclassification adjustment for gains included in net income, net of tax of approximately $2,238 and $1,299 for the nine months ended September 30, 2014 and 2013, respectively.								(1,673)	(1,673)
Net income							25,804		25,804
Cash dividends declared and paid on common shares ($0.45 and $0.39 per common share for the nine months ended September 30, 2014 and 2013, respectively)							(11,747)
Repurchase of outstanding shares	(13,152)	(4,075)	(912)
Award of common shares released from Employee Benefit Trust (133,446 and 141,059 common shares for the nine months ended September 30, 2014 and 2013, respectively)					1,608
Shares issued upon vesting of restricted stock unit awards					161	2,338	(100)
Issuance upon exercise of stock options					849	4,262	(126)		4,074
Stock-based compensation activity, net					(284)
Stock-based income tax benefit					339
Balance, end of period at Sep. 30, 2013				315	200,987	(21,796)	255,687	(8,181)	427,012
Balance, beginning of period at Dec. 31, 2013				315	201,902	(22,053)	263,743	(11,375)	432,532
Change in net unrealized gains (losses) on securities available for sale, net of taxes of approximately ($7,484) and $15,482 for the nine months ended September 30, 2014 and 2013, respectively								9,667	9,667
Amortization of actuarial losses, net of taxes of approximately ($266) and ($405) for the nine months ended September 30, 2014 and 2013, respectively								259	(259)
Amortization of prior service credits, net of taxes of approximately $18 and $15 for the nine months ended September 30, 2014 and 2013, respectively								(16)	16
Reclassification adjustment for gains included in net income, net of tax of approximately $2,238 and $1,299 for the nine months ended September 30, 2014 and 2013, respectively.								(2,978)	(2,978)
Net income							33,182		33,182
Cash dividends declared and paid on common shares ($0.45 and $0.39 per common share for the nine months ended September 30, 2014 and 2013, respectively)							(13,461)
Repurchase of outstanding shares	(12,660)	(1,290)	(1,145)
Award of common shares released from Employee Benefit Trust (133,446 and 141,059 common shares for the nine months ended September 30, 2014 and 2013, respectively)					2,029
Shares issued upon vesting of restricted stock unit awards					30	3,137	(405)
Issuance upon exercise of stock options					310	1,697	(50)		1,290
Stock-based compensation activity, net					801
Stock-based income tax benefit					757
Balance, end of period at Sep. 30, 2014				$ 315	$ 205,829	$ (32,314)	$ 283,009	$ (4,443)	$ 452,396