Impairment of Investment Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Other than temporary impairment charges recognized	$ 0	$ 0
Amortized Cost	805,149,000		$ 924,054,000
Securities available for sale, at fair value	812,383,000		909,247,000
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,003,000		28,054,000
Federal Home Loan Bank Stock	9,900,000		30,500,000
Other Investments and Securities, at Cost	$ 1,700,000		1,700,000
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	40
Corporate Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Securities available for sale, at fair value	$ 24,035,000		21,012,000
Equity Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Other than temporary impairment charges recognized	$ 0	$ 0
US Government-sponsored Enterprises Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Percent of Unrealized Losses	96.00%
US Government Agencies Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Percent of Unrealized Losses	4.00%
Corporate Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Amortized Cost	$ 22,914,000		20,912,000
Securities available for sale, at fair value	$ 24,035,000		$ 21,012,000
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	0		4