Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (Loss) Income, Net of Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance			$ (22,144)
Cumulative effect on retained earnings	$ 756,023	$ 669,107	756,023	$ 669,107	$ 739,998	$ 692,472	$ 654,873	$ 675,122
Other comprehensive (loss) income	(528)	707	2,071	2,393
Ending balance	(20,073)		(20,073)
Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings								(11,047)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance			(1,379)	(3,231)
Other comprehensive (loss) income			1,114	1,980
Ending balance	(265)	(1,014)	(265)	(1,014)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member] | Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings								237
Net Change Related to Derivatives Used for Cash Flow Hedge [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance			(421)	(185)
Other comprehensive (loss) income			177	(299)
Ending balance	(244)	(484)	(244)	(484)
Net Change Related to Derivatives Used for Cash Flow Hedge [Member] | Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings								0
Net Change Related to Defined Benefit Pension Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance			(20,344)	(18,314)
Other comprehensive (loss) income			780	712
Ending balance	(19,564)	(17,602)	(19,564)	(17,602)
Net Change Related to Defined Benefit Pension Plan [Member] | Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings								0
Accumulated Other Comprehensive (Loss) Income [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance			(22,144)	(21,730)
Cumulative effect on retained earnings	(20,073)	(19,100)	(20,073)	(19,100)	$ (19,545)	$ (22,144)	$ (19,807)	(21,730)
Other comprehensive (loss) income	(528)	707	2,071	2,393
Ending balance	$ (20,073)	$ (19,100)	$ (20,073)	$ (19,100)
Accumulated Other Comprehensive (Loss) Income [Member] | Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings								$ 237