Derivatives and Hedging Activities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Derivative	Dec. 31, 2019 USD ($) Derivative	Dec. 31, 2018 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain (loss) on change in fair value	$ (8,750,000)	$ (2,536,000)	$ 131,000
Collateral posted with market value on liability positions with credit risk-related contingent features	$ 84,600,000
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	112	65
Aggregate notional amount	$ 649,900,000	$ 399,900,000
Net gain (loss) on change in fair value	(2,000,000.0)	(1,100,000)	(400,000)
Income (loss) on derivative instrument not designated hedges	$ 8,100,000	$ 4,500,000	2,100,000
Risk Participation in Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	12	10
Aggregate notional amount	$ 101,100,000	$ 96,500,000
Risk Participation out Agreement [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	1	1
Aggregate notional amount	$ 10,000,000.0	$ 7,000,000.0
Other Contract [Member] | Forward TBA Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate notional amount	183,500,000	50,000,000.0
Net gain (loss) on change in fair value	$ (7,400,000)	$ (1,400,000)	$ 400,000