Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 1,519	$ 686	$ 1,519	$ 686
With no required reserve recorded, Unpaid Balance Principal	1,868	1,024	1,868	1,024
With no required reserve recorded, Average Carrying Value Recognized	895	698	629	704
With no required reserve recorded, Interest Income	6		13
With required reserve recorded, Carrying Value	2,394	5,086	2,394	5,086
With required reserve recorded, Unpaid Balance Principal	2,394	5,086	2,394	5,086
With required reserve recorded, Required Reserve	333	713	333	713
With required reserve recorded, Average Carrying Value Recognized	2,562	5,091	2,726	5,100
With required reserve recorded, Interest Income	20	57	40	91
Carrying Value	3,913	5,772	3,913	5,772
Unpaid Balance Principal	4,262	6,110	4,262	6,110
With required reserve recorded, Required Reserve	333	713	333	713
Average Carrying Value Recognized	3,457	5,789	3,355	5,804
Interest Income	26	57	53	91
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	78	162	78	162
With no required reserve recorded, Unpaid Balance Principal	283	366	283	366
With no required reserve recorded, Average Carrying Value Recognized	83	170	84	170
With no required reserve recorded, Interest Income	1		2
With required reserve recorded, Carrying Value	470	430	470	430
With required reserve recorded, Unpaid Balance Principal	470	430	470	430
With required reserve recorded, Required Reserve	248	47	248	47
With required reserve recorded, Average Carrying Value Recognized	349	431	317	433
With required reserve recorded, Interest Income	3	7	6	12
Carrying Value	548	592	548	592
Unpaid Balance Principal	753	796	753	796
With required reserve recorded, Required Reserve	248	47	248	47
Average Carrying Value Recognized	432	601	401	603
Interest Income	4	7	8	12
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	1,441	524	1,441	524
With no required reserve recorded, Unpaid Balance Principal	1,585	658	1,585	658
With no required reserve recorded, Average Carrying Value Recognized	812	528	545	534
With no required reserve recorded, Interest Income	5		11
With required reserve recorded, Carrying Value	1,924	1,981	1,924	1,981
With required reserve recorded, Unpaid Balance Principal	1,924	1,981	1,924	1,981
With required reserve recorded, Required Reserve	85	91	85	91
With required reserve recorded, Average Carrying Value Recognized	2,213	1,985	2,409	1,992
With required reserve recorded, Interest Income	17	40	34	63
Carrying Value	3,365	2,505	3,365	2,505
Unpaid Balance Principal	3,509	2,639	3,509	2,639
With required reserve recorded, Required Reserve	85	91	85	91
Average Carrying Value Recognized	3,025	2,513	2,954	2,526
Interest Income	22	40	45	63
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With required reserve recorded, Carrying Value		2,675		2,675
With required reserve recorded, Unpaid Balance Principal		2,675		2,675
With required reserve recorded, Required Reserve	575	575	575	575
With required reserve recorded, Average Carrying Value Recognized		2,675		2,675
With required reserve recorded, Interest Income		10		16
Carrying Value		2,675		2,675
Unpaid Balance Principal		2,675		2,675
With required reserve recorded, Required Reserve	$ 575	575	$ 575	575
Average Carrying Value Recognized		2,675		2,675
Interest Income		$ 10		$ 16