Accumulated Other Comprehensive (Loss) Income - Amounts Reclassified Out of Each Component of Accumulated Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of investment securities	$ 181	$ 415	$ 272	$ 557
Amortization of net loss included in net periodic pension costs	340	167	681	331
Accretion of prior service cost included in net periodic pension costs	(70)	(69)	(140)	(144)
Income before income taxes	8,758	6,627	17,008	14,358
Tax (expense) benefit	(2,292)	(1,547)	(4,426)	(3,552)
Net income	6,466	5,080	12,582	10,806
Amount Reclassified from Accumulated Other Comprehensive (Loss) Income [Member] | Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of investment securities	181	415	272	557
Income before income taxes	181	415	272	557
Tax (expense) benefit	(63)	(145)	(95)	(195)
Net income	118	270	177	362
Amount Reclassified from Accumulated Other Comprehensive (Loss) Income [Member] | Net Change Related to Defined Benefit Pension Plan [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net loss included in net periodic pension costs	(340)	(167)	(681)	(331)
Accretion of prior service cost included in net periodic pension costs	70	69	140	144
Income before income taxes	(270)	(98)	(541)	(187)
Tax (expense) benefit	94	34	190	65
Net income	$ (176)	$ (64)	$ (351)	$ (122)