Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period			$ (24,881)
Other comprehensive income (loss), net of tax	$ 14,840	$ (5,721)	26,347	$ (22,697)
Balance at the end of the period	1,466	(36,071)	1,466	(36,071)
Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(6,355)	(7,607)	(6,450)	(5,998)
Amounts reclassified from accumulated other comprehensive income (loss)	6,058	151	6,153	302
Other comprehensive income (loss), net of tax	6,058	151	6,153	302
AOCI reclassification to retained earnings from adoption of ASU 2018-02				(1,760)
Balance at the end of the period	(297)	(7,456)	(297)	(7,456)
Unrealized Gains and Losses on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(4,906)	(22,617)	(18,394)	(4,278)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	19,183	(6,409)	33,092	(23,601)
Amounts reclassified from accumulated other comprehensive income (loss)	(1,333)	500	(1,754)	500
Other comprehensive income (loss), net of tax	17,850	(5,909)	31,338	(23,101)
AOCI reclassification to retained earnings from adoption of ASU 2018-02				(1,147)
Balance at the end of the period	12,944	(28,526)	12,944	(28,526)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(2,113)	(126)	(37)	(151)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(8,795)	6	(10,876)	34
Amounts reclassified from accumulated other comprehensive income (loss)	(273)	31	(268)	68
Other comprehensive income (loss), net of tax	(9,068)	37	(11,144)	102
AOCI reclassification to retained earnings from adoption of ASU 2018-02				(40)
Balance at the end of the period	(11,181)	(89)	(11,181)	(89)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(13,374)	(30,350)	(24,881)	(10,427)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	10,388	(6,403)	22,216	(23,567)
Amounts reclassified from accumulated other comprehensive income (loss)	4,452	682	4,131	870
Other comprehensive income (loss), net of tax	14,840	(5,721)	26,347	(22,697)
AOCI reclassification to retained earnings from adoption of ASU 2018-02				(2,947)
Balance at the end of the period	$ 1,466	$ (36,071)	$ 1,466	$ (36,071)