CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income
Beginning Balance at Dec. 31, 2011	$ 218,876	$ 51,438	$ 165,377	$ 2,061
Beginning Balance (in shares) at Dec. 31, 2011		7,664,975
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,995		12,995
Other comprehensive income (loss), net of tax:
Change in fair value of securities available-for-sale	954			954
Change in fair value of cash flow hedges	(754)			(754)
Change in net unrecognized losses on postretirement plans	54			54
Comprehensive income (loss)	13,249		12,995	254
Stock-based compensation expense	172	172
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings and tax benefit		19,614
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings and tax benefit	(240)	(240)
Common stock repurchased (in shares)		(65,580)
Common stock repurchased	(2,097)	(2,097)
Cash dividends declared ($0.50 per share)	(3,872)		(3,872)
Ending Balance at Jun. 30, 2012	226,088	49,273	174,500	2,315
Ending Balance (in shares) at Jun. 30, 2012		7,619,009
Beginning Balance at Dec. 31, 2012	233,815	49,667	181,151	2,997
Beginning Balance (in shares) at Dec. 31, 2012		7,622,750
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,993		11,993
Other comprehensive income (loss), net of tax:
Change in fair value of securities available-for-sale	(15,533)			(15,533)
Change in fair value of cash flow hedges	3,146			3,146
Change in net unrecognized losses on postretirement plans	94			94
Comprehensive income (loss)	(300)		11,993	(12,293)
Stock-based compensation expense	159	159
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings and tax benefit		17,962
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings and tax benefit	83	83
Cash dividends declared ($0.50 per share)	(4,137)		(4,137)
Ending Balance at Jun. 30, 2013	$ 229,620	$ 49,909	$ 189,007	$ (9,296)
Ending Balance (in shares) at Jun. 30, 2013		7,640,712