Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 10,089	$ 8,250
Net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount
Net unrealized holding gains (losses) arising during the period, Before Tax Amount	2,218	2,158
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(44)	(91)
Total net unrealized gains on available-for-sale investment securities, Before Tax Amount	2,174	2,067
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(545)	(337)
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	329	341
Accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(71)	(70)
Total defined benefit pension plans, Before Tax Amount	258	271
Other comprehensive income (loss), Before Tax Amount	1,887	2,001
Total comprehensive income (loss), Before Tax Amount	11,976	10,251
Tax (expense) benefit	2,800	2,134
Net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period, Tax Expense (Benefit)	776	755
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(15)	(32)
Total net unrealized gains on available-for-sale investment securities, Tax Expense (Benefit)	761	723
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(191)	(118)
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	115	120
Accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(25)	(24)
Total defined benefit pension plans, Tax Expense (Benefit)	90	96
Other comprehensive income (loss), Tax Expense (Benefit)	660	701
Total comprehensive income (loss), Tax Expense (Benefit)	3,460	2,835
Net income	7,289	6,116
Net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding gains (losses) arising during the period, Net of Tax Amount	1,442	1,403
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(29)	(59)
Total net unrealized gains on available-for-sale investment securities, Net of Tax Amount	1,413	1,344
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(354)	(219)
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	214	221
Accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(46)	(46)
Total defined benefit pension plans, Net of Tax Amount	168	175
Other comprehensive income (loss), Net of Tax Amount	1,227	1,300
Total comprehensive income (loss), Net of Tax Amount	$ 8,516	$ 7,416