Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income [Abstract]
Net income	$ 11,260	$ 6,637	$ 8,019	$ 7,571	$ 7,281	$ 7,037	$ 6,345	$ 5,974	$ 33,487	$ 26,637	$ 25,632
Securities available for sale:
Unrealized holding gains (losses) on securities									(6,869)	3,305	22,443
Non-credit related portion of other-than-temporary impairment on securities									0	0	(9,376)
Reclassification adjustment for gains realized in net income									71	(1,170)	(2,961)
Amortization of unrealized holding gains on securities transferred to the held to maturity category									(215)	(350)	(617)
Total securities available for sale									(7,013)	1,785	9,489
Derivative instruments:
Unrealized holding (losses) gains on derivative instruments									1,325	(1,336)	0
Reclassification adjustment for gains realized in net income									(125)	(311)	(377)
Totals derivative instruments									1,200	(1,647)	(377)
Defined benefit pension and post-retirement benefit plans:
Net (loss) gain arising during the period									1,957	(756)	(1,092)
Less amortization of net actuarial loss recognized in net periodic pension cost									384	264	274
Total defined benefit pension and post-retirement benefit plans									2,341	(492)	(818)
Other comprehensive (loss) income, net of tax									(3,472)	(354)	8,294
Comprehensive income									$ 30,015	$ 26,283	$ 33,926