Investment Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	$ 0	$ 0
Gain Losses Maturities And Impairment	2,000	6,000
Available-for-sale Securities, Gross Realized Gains	0	0
Gross Losses	0	0
Gross Gains	2,000	6,000
Debt Securities, Held-to-maturity, Restricted	347,600,000		$ 313,900,000
Proceeds from Sale of Available-for-sale Securities	0	0
Debt Securities, Available-for-sale, Restricted	$ 675,500,000		759,100,000
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	165
Amortized Cost	$ 994,657,000		1,045,579,000
Available-for-sale Securities	933,204,000		1,041,380,000
Other than temporary impairment charges recognized	0	0
Other Investments and Securities, at Cost	1,200,000		1,200,000
Federal Home Loan Bank Stock	$ 12,000,000		$ 11,700,000
US Government-sponsored Enterprises Debt Securities [Member]
Percent of Unrealized Losses	97.00%
Corporate Debt Securities [Member]
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	4		4
Amortized Cost	$ 32,100,000		$ 32,100,000
Available-for-sale Securities	31,800,000		$ 32,900,000
Equity Securities [Member]
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount	$ 0	$ 0