Qualified Affordable Housing Project Investments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investments In Affordable Housing Projects [Abstract]
Investment for qualified affordable housing projects included in other assets	$ 4,669,000		$ 4,669,000		$ 4,276,000
Unfunded commitments related to the investments in qualified affordable housing projects	4,173,000		4,173,000		$ 4,922,000
Recognized amortization expense	133,000	$ 130,000	399,000	$ 388,000
Recognized tax credits and other benefits from its investment in affordable housing tax credits	275,000	207,000	827,000	633,000
Impairment losses related to its investment in qualified affordable housing projects	$ 0	$ 0	$ 0	$ 0