Mortgage Banking Activities - Valuation Allowance for Mortgage Servicing Rights (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Mortgage Banking [Abstract]
Balance, beginning of period	$ (1,565,000)	$ (20,000)	$ (70,000)	$ (9,000)
Impairment charges	(336,000)	(6,000)	(1,831,000)	(26,000)
Recoveries				9,000
Balance, end of period	$ (1,901,000)	$ (26,000)	$ (1,901,000)	$ (26,000)