Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	$ (24,881)
Other comprehensive gain (loss), net of tax	11,507	$ (16,976)
Balance at the end of the period	(13,374)	(30,350)
Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(6,450)	(5,998)
Amounts reclassified from accumulated other comprehensive income (loss)	95	151
Other comprehensive gain (loss), net of tax	95	151
AOCI reclassification to retained earnings from adoption of ASU 2018-02		(1,760)
Balance at the end of the period	(6,355)	(7,607)
Unrealized Gains and Losses on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(18,394)	(4,278)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	13,066	(17,192)
Amounts reclassified from accumulated other comprehensive income (loss)	422
Other comprehensive gain (loss), net of tax	13,488	(17,192)
AOCI reclassification to retained earnings from adoption of ASU 2018-02		(1,147)
Balance at the end of the period	(4,906)	(22,617)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(37)	(151)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(2,068)	28
Amounts reclassified from accumulated other comprehensive income (loss)	(8)	37
Other comprehensive gain (loss), net of tax	(2,076)	65
AOCI reclassification to retained earnings from adoption of ASU 2018-02		(40)
Balance at the end of the period	(2,113)	(126)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(24,881)	(10,427)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	10,998	(17,164)
Amounts reclassified from accumulated other comprehensive income (loss)	509	188
Other comprehensive gain (loss), net of tax	11,507	(16,976)
AOCI reclassification to retained earnings from adoption of ASU 2018-02		(2,947)
Balance at the end of the period	$ (13,374)	$ (30,350)