Accumulated Other Comprehensive Income (Loss) (''AOCI'') - Changes in AOCI by Component (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Changes in AOCI by Component
Balance at the beginning of the period, net of taxes			$ (9,252)
Amounts reclassified from other comprehensive income (loss), net of taxes	$ 32	$ 22	(91)	$ 71
Net current period other comprehensive income (loss), net of taxes	(1,307)	327	(7,921)	1,774
Balance at the end of the period, net of taxes	(17,173)		(17,173)
Accumulated Other Comprehensive Income / (Loss)
Changes in AOCI by Component
Balance at the beginning of the period, net of taxes	(15,866)	(6,467)	(9,252)	(7,914)
Other comprehensive income (loss) before reclassification, net of taxes	(1,339)	305	(7,830)	1,703
Amounts reclassified from other comprehensive income (loss), net of taxes	32	22	(91)	71
Net current period other comprehensive income (loss), net of taxes	(1,307)	327	(7,921)	1,774
Balance at the end of the period, net of taxes	(17,173)	(6,140)	(17,173)	(6,140)
Unrealized Gains (Losses) on Available-for-Sale Securities and I/O Strips
Changes in AOCI by Component
Balance at the beginning of the period, net of taxes	(7,031)	877	(362)	(540)
Other comprehensive income (loss) before reclassification, net of taxes	(1,335)	312	(7,817)	1,725
Amounts reclassified from other comprehensive income (loss), net of taxes			(187)	4
Net current period other comprehensive income (loss), net of taxes	(1,335)	312	(8,004)	1,729
Balance at the end of the period, net of taxes	(8,366)	1,189	(8,366)	1,189
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity
Changes in AOCI by Component
Balance at the beginning of the period, net of taxes	359	321	375	336
Amounts reclassified from other comprehensive income (loss), net of taxes	(8)	(7)	(24)	(22)
Net current period other comprehensive income (loss), net of taxes	(8)	(7)	(24)	(22)
Balance at the end of the period, net of taxes	351	314	351	314
Defined Benefit Pension Plan Items
Changes in AOCI by Component
Balance at the beginning of the period, net of taxes	(9,194)	(7,665)	(9,265)	(7,710)
Other comprehensive income (loss) before reclassification, net of taxes	(4)	(7)	(13)	(22)
Amounts reclassified from other comprehensive income (loss), net of taxes	40	29	120	89
Net current period other comprehensive income (loss), net of taxes	36	22	107	67
Balance at the end of the period, net of taxes	$ (9,158)	$ (7,643)	$ (9,158)	$ (7,643)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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