Mortgage Banking Activities - Valuation Allowance for Mortgage Servicing Rights (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Mortgage Banking [Abstract]
Balance, beginning of period	$ (70,000)	$ (9,000)
Impairment charges	(499,000)
Recoveries		$ 9,000
Balance, end of period	$ (569,000)