Derivatives and Hedging Activities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) Derivative	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) Derivative	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Derivative
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain (loss) on change in fair value	$ (2,088,000)	$ (402,000)	$ 4,175,000	$ (5,955,000)
Collateral posted with market value on liability positions with credit risk-related contingent features	$ 63,700,000		$ 63,700,000
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	129		129		112
Aggregate notional amount	$ 723,700,000		$ 723,700,000		$ 649,900,000
Income (loss) on derivative instrument not designated hedges	$ 1,000,000.0	$ 3,500,000	$ 2,900,000	$ 6,100,000
Risk Participation in Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	13		13		12
Aggregate notional amount	$ 118,500,000		$ 118,500,000		$ 101,100,000
Risk Participation out Agreement [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest rate swaps | Derivative	1		1		1
Aggregate notional amount	$ 10,000,000.0		$ 10,000,000.0		$ 10,000,000.0
Other Contract [Member] | Forward TBA Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate notional amount	$ 83,000,000.0		$ 83,000,000.0		$ 183,500,000