Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period			$ (10,427)
Net comprehensive income (loss)	$ (5,721)	$ 1,187	(22,697)	$ 4,514
Balance at the end of the period	(36,071)	(3,697)	(36,071)	(3,697)
Amortization of defined benefit pension
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(7,607)	(6,078)	(5,998)	(6,195)
Amounts reclassified from accumulated other comprehensive income (loss)	151	116	302	233
Net comprehensive income (loss)	151	116	302	233
Balance at the end of the period	(7,456)	(5,962)	(7,456)	(5,962)
Amortization of defined benefit pension | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(1,760)
Unrealized gains and losses on securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(22,617)	1,458	(4,278)	(1,708)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(6,409)	1,115	(23,601)	4,282
Amounts reclassified from accumulated other comprehensive income (loss)	500	(67)	500	(68)
Net comprehensive income (loss)	(5,909)	1,048	(23,101)	4,214
Balance at the end of the period	(28,526)	2,506	(28,526)	2,506
Unrealized gains and losses on securities | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(1,147)
Gains on sales of available for sale securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(126)	(264)	(151)	(308)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	6	11	34	(37)
Amounts reclassified from accumulated other comprehensive income (loss)	31	12	68	104
Net comprehensive income (loss)	37	23	102	67
Balance at the end of the period	(89)	(241)	(89)	(241)
Gains on sales of available for sale securities | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(40)
Accumulated Other Comprehensive Income (Loss).
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(30,350)	(4,884)	(10,427)	(8,211)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(6,403)	1,126	(23,567)	4,245
Amounts reclassified from accumulated other comprehensive income (loss)	682	61	870	269
Net comprehensive income (loss)	(5,721)	1,187	(22,697)	4,514
Balance at the end of the period	$ (36,071)	$ (3,697)	(36,071)	$ (3,697)
Accumulated Other Comprehensive Income (Loss). | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(2,947)
Amounts reclassified from accumulated other comprehensive income (loss)			$ (2,947)