Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Before-Tax Amount
Net unrealized gains		$ 3,433	$ 8,456	$ 5,806	$ 29,552
Tax (Expense) Benefit
Net unrealized gains		(1,373)	(3,382)	(2,321)	(11,818)
Net of Tax
Net current-period other comprehensive income		2,060	5,074	3,485	17,734
Available-for-sale securities:
Before-Tax Amount
Change in net unrealized gain/loss during the period		3,051	8,362	5,044	29,317
Reclassification adjustment for net realized gain on sale of available-for-sale securities included in net income		0	(240)	0	(472)
Net unrealized gains		3,051	8,122	5,044	28,845
Tax (Expense) Benefit
Change in net unrealized gain/loss during the period		(1,220)	(3,344)	(2,016)	(11,724)
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		0	96	0	189
Net unrealized gains		(1,220)	(3,248)	(2,016)	(11,535)
Net of Tax
Change in net unrealized gain/loss during the period		1,831	5,018	3,028	17,593
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		0	(144)	0	(283)
Net current-period other comprehensive income		1,831	4,874	3,028	17,310
Plan actuarial loss
Before-Tax Amount
Reclassification adjustment for net realized gain on sale of available-for-sale securities included in net income	[1],[2]	397	326	754	669
Tax (Expense) Benefit
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		(159)	(131)	(302)	(268)
Net of Tax
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		238	195	452	401
Net retirement plan prior service (cost) credit
Before-Tax Amount
Reclassification adjustment for net realized gain on sale of available-for-sale securities included in net income	[1],[2]	(15)	8	8	38
Tax (Expense) Benefit
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		6	(3)	(3)	(15)
Net of Tax
Reclassification adjustment for net realized gain on sale included in available-for-sale securities		(9)	5	5	23
Employee benefit plans
Before-Tax Amount
Reclassification adjustment for net realized gain on sale of available-for-sale securities included in net income	[1]	382	334	762	707
Net unrealized gains		382	334	762	707
Tax (Expense) Benefit
Reclassification adjustment for net realized gain on sale included in available-for-sale securities	[1]	(153)	(134)	(305)	(283)
Net unrealized gains		(153)	(134)	(305)	(283)
Net of Tax
Change in net unrealized gain/loss during the period		0	0	0	0
Reclassification adjustment for net realized gain on sale included in available-for-sale securities	[1]	229	200	457	424
Net current-period other comprehensive income		$ 229	$ 200	$ 457	$ 424

[1] Amounts in parentheses indicated debits in income statement.

[2] The accumulated other comprehensive (loss) income components are included in the computation of net periodic benefit cost (See Note 10 - “Employee Benefit Plan”).