Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	$ (10,427)
Net comprehensive income (loss)	(16,976)	$ 3,327
Balance at the end of the period	(30,350)	(4,884)
Amortization of defined benefit pension
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(5,998)	(6,195)
Amounts reclassified from accumulated other comprehensive income (loss)	151	117
Net comprehensive income (loss)	151	117
Balance at the end of the period	(7,607)	(6,078)
Amortization of defined benefit pension | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from accumulated other comprehensive income (loss)	(1,760)
Unrealized gains and losses on securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(4,278)	(1,708)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(17,192)	3,166
Net comprehensive income (loss)	(17,192)	3,166
Balance at the end of the period	(22,617)	1,458
Unrealized gains and losses on securities | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from accumulated other comprehensive income (loss)	(1,147)
Gains on sales of available for sale securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(151)	(308)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	28	(24)
Amounts reclassified from accumulated other comprehensive income (loss)	37	68
Net comprehensive income (loss)	65	44
Balance at the end of the period	(126)	(264)
Gains on sales of available for sale securities | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from accumulated other comprehensive income (loss)	(40)
Accumulated Other Comprehensive Income (Loss).
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(10,427)	(8,211)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(17,164)	3,142
Amounts reclassified from accumulated other comprehensive income (loss)	188	185
Net comprehensive income (loss)	(16,976)	3,327
Balance at the end of the period	(30,350)	$ (4,884)
Accumulated Other Comprehensive Income (Loss). | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from accumulated other comprehensive income (loss)	$ (2,947)