Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period			$ (8,211)
Other comprehensive income (loss), net of tax	$ (91)	$ (2,515)	4,423	$ 7,866
Balance at the end of the period	(3,788)	3,995	(3,788)	3,995
Amortization of defined benefit pension
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(5,962)	(5,762)	(6,195)	(6,015)
Amounts reclassified from accumulated other comprehensive income (loss)	116	126	349	379
Other comprehensive income (loss), net of tax	116	126	349	379
Balance at the end of the period	(5,846)	(5,636)	(5,846)	(5,636)
Unrealized gains and losses on securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	2,506	12,752	(1,708)	2,588
Other comprehensive income (loss) before reclassifications	80	(2,715)	4,362	7,524
Amounts reclassified from accumulated other comprehensive income (loss)	(325)		(393)	(75)
Other comprehensive income (loss), net of tax	(245)	(2,715)	3,969	7,449
Balance at the end of the period	2,261	10,037	2,261	10,037
Gains on sales of available for sale securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(241)	(480)	(308)	(444)
Other comprehensive income (loss) before reclassifications	3	32	(35)	(91)
Amounts reclassified from accumulated other comprehensive income (loss)	35	42	140	129
Other comprehensive income (loss), net of tax	38	74	105	38
Balance at the end of the period	(203)	(406)	(203)	(406)
Accumulated Other Comprehensive Income (Loss).
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(3,697)	6,510	(8,211)	(3,871)
Other comprehensive income (loss) before reclassifications	83	(2,683)	4,327	7,433
Amounts reclassified from accumulated other comprehensive income (loss)	(174)	168	96	433
Other comprehensive income (loss), net of tax	(91)	(2,515)	4,423	7,866
Balance at the end of the period	$ (3,788)	$ 3,995	$ (3,788)	$ 3,995