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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance				$ (21,730)
Cumulative effect on retained earnings		$ 669,107	$ 664,299	669,107	$ 664,299	$ 654,873	$ 675,122	$ 651,670	$ 624,133
Other comprehensive (loss) income		707	(59)	2,393	6,325
Ending balance		(19,100)		(19,100)
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)
Accounting Standards Update 2017-12 | 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 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				(3,231)	(11,221)
Other comprehensive (loss) income				1,980	6,157
Ending balance		(1,014)	(5,064)	(1,014)	(5,064)
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	[1]						237
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member] | Accounting Standards Update 2017-12 | 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 Derivatives Used for Cash Flow Hedge [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance				(185)	81
Other comprehensive (loss) income				(299)	(421)
Ending balance		(484)	(257)	(484)	(257)
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	[1]						0
Net Change Related to Derivatives Used for Cash Flow Hedge [Member] | Accounting Standards Update 2017-12 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings									83
Net Change Related to Defined Benefit Pension Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance				(18,314)	(17,276)
Other comprehensive (loss) income				712	589
Ending balance		(17,602)	(16,687)	(17,602)	(16,687)
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	[1]						0
Net Change Related to Defined Benefit Pension Plan [Member] | Accounting Standards Update 2017-12 | 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				(21,730)	(28,416)
Cumulative effect on retained earnings		(19,100)	(22,008)	(19,100)	(22,008)	$ (19,807)	(21,730)	$ (21,949)	(28,416)
Other comprehensive (loss) income		707	(59)	2,393	6,325
Ending balance		$ (19,100)	$ (22,008)	$ (19,100)	$ (22,008)
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	[1]						$ 237
Accumulated Other Comprehensive (Loss) Income [Member] | Accounting Standards Update 2017-12 | Cumulative Effect, Period Of Adoption, Adjustment
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative effect on retained earnings									$ 83

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2020" for additional information.