Consolidated Statements of Changes in Stockholders’ Equity (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member] Shares Purchased To Fund Options Exercised [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Purchase of Common Shares Outstanding [Member]	Restricted Stock Awards Repurchased To Satisfy Tax Obligations [Member]	Total
Balance at Dec. 31, 2011	$ 315	$ 195,628		$ (7,355)	$ 223,510	$ 4,813
Common Stock
Amortization of prior service credits, net of taxes of $19, $20 and $20 for the years ended December 31, 2014, 2013 and 2012, respectively						(26)
Amortization of net actuarial losses, net of taxes of ($330), ($541) and ($456) for the years ended December 31, 2014, 2013 and 2012, respectively						587			(587)
Unrecognized actuarial gains (losses), net of taxes of $2,880, ($2,527) and $340 for the years ended December 31, 2014, 2013 and 2012, respectively						(479)			(479)
Change in net unrealized (losses) gains on securities available for sale, net of taxes of approximately ($10,441), $20,609 and ($5,259) for the years ended December 31, 2014, 2013 and 2012, respectively						6,831			6,831
Reclassification adjustment for (gains) losses included in net income, net of taxes of approximately $1,241, $700 and ($318) for the years ended December 31, 2014, 2013 and 2012, respectively						411			26
Net income					34,331				34,331
Award of common shares released from Employee Benefit Trust (136,559, 143,941 and 157,922 common shares for the years ended December 31, 2014, 2013 and 2012, respectively)		1,480
Value of shares issued upon vesting of restricted stock unit awards		317		1,737	(105)
Cash dividends declared and paid on common shares ($0.60, $0.52 and $0.52 per share for the years ended December 31, 2014, 2013 and 2012, respectively)					(15,817)
Value of stock options exercised		164		1,818	(63)				905
Stock-based compensation activity, net		1,028
Stock-based income tax (provision) benefit		(303)
Treasury Stock
Value of shares purchased for the Treasury			(906)				(5,019)	(532)
Balance at Dec. 31, 2012	315	198,314		(10,257)	241,856	12,137			442,365
Common Stock
Amortization of prior service credits, net of taxes of $19, $20 and $20 for the years ended December 31, 2014, 2013 and 2012, respectively						(26)
Amortization of net actuarial losses, net of taxes of ($330), ($541) and ($456) for the years ended December 31, 2014, 2013 and 2012, respectively						696			(696)
Unrecognized actuarial gains (losses), net of taxes of $2,880, ($2,527) and $340 for the years ended December 31, 2014, 2013 and 2012, respectively						3,261			3,261
Change in net unrealized (losses) gains on securities available for sale, net of taxes of approximately ($10,441), $20,609 and ($5,259) for the years ended December 31, 2014, 2013 and 2012, respectively						(26,541)			(26,541)
Reclassification adjustment for (gains) losses included in net income, net of taxes of approximately $1,241, $700 and ($318) for the years ended December 31, 2014, 2013 and 2012, respectively						(902)			1,700
Net income					37,752				37,752
Award of common shares released from Employee Benefit Trust (136,559, 143,941 and 157,922 common shares for the years ended December 31, 2014, 2013 and 2012, respectively)		1,652
Value of shares issued upon vesting of restricted stock unit awards		161		2,406	(119)
Cash dividends declared and paid on common shares ($0.60, $0.52 and $0.52 per share for the years ended December 31, 2014, 2013 and 2012, respectively)					(15,618)
Value of stock options exercised		1,451		6,763	(128)				6,814
Stock-based compensation activity, net		(119)
Stock-based income tax (provision) benefit		443
Treasury Stock
Value of shares purchased for the Treasury			(6,814)				(13,152)	(999)
Balance at Dec. 31, 2013	315	201,902		(22,053)	263,743	(11,375)			432,532
Common Stock
Amortization of prior service credits, net of taxes of $19, $20 and $20 for the years ended December 31, 2014, 2013 and 2012, respectively						(26)
Amortization of net actuarial losses, net of taxes of ($330), ($541) and ($456) for the years ended December 31, 2014, 2013 and 2012, respectively						370			(370)
Unrecognized actuarial gains (losses), net of taxes of $2,880, ($2,527) and $340 for the years ended December 31, 2014, 2013 and 2012, respectively						(3,790)			(3,790)
Change in net unrealized (losses) gains on securities available for sale, net of taxes of approximately ($10,441), $20,609 and ($5,259) for the years ended December 31, 2014, 2013 and 2012, respectively						13,548			13,548
Reclassification adjustment for (gains) losses included in net income, net of taxes of approximately $1,241, $700 and ($318) for the years ended December 31, 2014, 2013 and 2012, respectively						(1,634)			1,634
Net income					44,239				44,239
Award of common shares released from Employee Benefit Trust (136,559, 143,941 and 157,922 common shares for the years ended December 31, 2014, 2013 and 2012, respectively)		2,075
Value of shares issued upon vesting of restricted stock unit awards		30		3,205	(430)
Cash dividends declared and paid on common shares ($0.60, $0.52 and $0.52 per share for the years ended December 31, 2014, 2013 and 2012, respectively)					(17,853)
Value of stock options exercised		455		2,461	(77)				1,962
Stock-based compensation activity, net		1,129
Stock-based income tax (provision) benefit		846
Treasury Stock
Value of shares purchased for the Treasury			(1,962)				(17,644)	(1,228)
Balance at Dec. 31, 2014	$ 315	$ 206,437		$ (37,221)	$ 289,622	$ (2,907)			$ 456,247