Allowance for Loan Losses - ALL by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 7,113	$ 4,241	$ 7,770	$ 3,863
Charge-offs	(472)	(441)	(1,379)	(915)
Recoveries	137	45	415	139
Provision (recovery)	509	1,075	481	1,833
Ending Balance	7,287	4,920	7,287	4,920
Mortgage Loans on Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	4,244	3,686	3,864	3,318
Charge-offs	(54)	(75)	(168)	(348)
Recoveries	60	10	103	98
Provision (recovery)	157	216	608	769
Ending Balance	4,407	3,837	4,407	3,837
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	944	456	878	493
Charge-offs			(116)
Recoveries		1	1	2
Provision (recovery)	186	56	367	18
Ending Balance	1,130	513	1,130	513
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	1,925	99	3,028	52
Charge-offs	(418)	(366)	(1,095)	(567)
Recoveries	77	34	311	39
Provision (recovery)	166	803	(494)	1,046
Ending Balance	$ 1,750	$ 570	$ 1,750	$ 570