Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 908,236		$ 908,236		$ 902,292
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	$ 0	0	$ 0
Impaired loans considered to be credit risk of non-collection	250		250
Updated appraisal requirement floor	250		250
Other real estate owned	1,079		1,079		2,228
Financial instrument of credit risk	100		100		$ 100
Fair Value, Assets Measured on Recurring Basis, Gain (Loss) Included in Other Income, Assets and Liabilities Continue to be held		0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	0
Total gains or losses included in earnings	0	245	0	198
Derivatives mark to market	(160)	(45)	(2,122)	(88)
Forward Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivatives mark to market	300		1,500
Forward Contracts [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivatives mark to market	(102)	201	132	122
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	0
Total gains or losses included in earnings	$ 0	$ 245	$ 0	$ 198
Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap Rates Term Used to Determine Yield Curve			3 years
Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap Rates Term Used to Determine Yield Curve			30 years