Impairment of Investment Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Other than temporary impairment charges recognized	$ 0	$ 0
Amortized Cost	898,877,000		$ 924,054,000
Securities available for sale, at fair value	893,101,000		909,247,000
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss	15,614,000		28,054,000
Federal Home Loan Bank Stock	$ 23,700,000		30,500,000
Other Investments and Securities, at Cost			1,700,000
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	98
Corporate Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Securities available for sale, at fair value	$ 23,549,000		21,012,000
Equity Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Other than temporary impairment charges recognized	$ 0	$ 0
Continuous Unrealized Loss Position, Fair Value			$ 0
US Government-sponsored Enterprises Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Percent of Unrealized Losses	79.00%