Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period			$ (10,427)
Net comprehensive income (loss)	$ (8,438)	$ (91)	(31,135)	$ 4,423
Balance at the end of the period	(44,509)	(3,788)	(44,509)	(3,788)
Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(7,456)	(5,962)	(5,998)	(6,195)
Amounts reclassified from accumulated other comprehensive income (loss)	151	116	453	349
Net comprehensive income (loss)	151	116	453	349
Balance at the end of the period	(7,305)	(5,846)	(7,305)	(5,846)
Benefit Plans | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(1,760)
Unrealized Gains and Losses on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(28,526)	2,506	(4,278)	(1,708)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(8,624)	80	(32,224)	4,362
Amounts reclassified from accumulated other comprehensive income (loss)	9	(325)	508	(393)
Net comprehensive income (loss)	(8,615)	(245)	(31,716)	3,969
Balance at the end of the period	(37,141)	2,261	(37,141)	2,261
Unrealized Gains and Losses on Securities Available for Sale | ASU 2018- 02
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications			(1,147)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(89)	(241)	(151)	(308)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1)	3	34	(35)
Amounts reclassified from accumulated other comprehensive income (loss)	27	35	94	140
Net comprehensive income (loss)	26	38	128	105
Balance at the end of the period	(63)	(203)	(63)	(203)
Gains and Losses on Cash Flow Hedges | 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	(36,071)	(3,697)	(10,427)	(8,211)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(8,625)	83	(32,190)	4,327
Amounts reclassified from accumulated other comprehensive income (loss)	187	(174)	1,055	96
Net comprehensive income (loss)	(8,438)	(91)	(31,135)	4,423
Balance at the end of the period	$ (44,509)	$ (3,788)	(44,509)	$ (3,788)
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)