Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 275		$ 276
With no required reserve recorded, Unpaid Balance Principal	512		503
With no required reserve recorded, Average Carrying Value Recognized	275	$ 314
With no required reserve recorded, Interest Income	2
With required reserve recorded, Carrying Value	2,991		2,775
With required reserve recorded, Unpaid Balance Principal	3,109		2,890
With required reserve recorded, Required Reserve	100	686	145
With required reserve recorded, Average Carrying Value Recognized	2,956	6,493
With required reserve recorded, Interest Income	27	34
Carrying Value	3,266	5,824	3,051
Unpaid Balance Principal	3,621		3,393
With required reserve recorded, Required Reserve	100	686	145
Average Carrying Value Recognized	3,231	6,807
Interest Income	29	34
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	93		87
With no required reserve recorded, Unpaid Balance Principal	306		291
With no required reserve recorded, Average Carrying Value Recognized	87	49
With no required reserve recorded, Interest Income	2
With required reserve recorded, Carrying Value	227		314
With required reserve recorded, Unpaid Balance Principal	228		315
With required reserve recorded, Required Reserve	6	12	54
With required reserve recorded, Average Carrying Value Recognized	262	388
With required reserve recorded, Interest Income	3	5
Carrying Value	320	522	401
Unpaid Balance Principal	534		606
With required reserve recorded, Required Reserve	6	12	54
Average Carrying Value Recognized	349	437
Interest Income	5	5
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	182		189
With no required reserve recorded, Unpaid Balance Principal	206		212
With no required reserve recorded, Average Carrying Value Recognized	188	265
With required reserve recorded, Carrying Value	2,764		2,461
With required reserve recorded, Unpaid Balance Principal	2,881		2,575
With required reserve recorded, Required Reserve	94	94	91
With required reserve recorded, Average Carrying Value Recognized	2,694	2,278
With required reserve recorded, Interest Income	24	23
Carrying Value	2,946	2,528	2,650
Unpaid Balance Principal	3,087		2,787
With required reserve recorded, Required Reserve	94	94	$ 91
Average Carrying Value Recognized	2,882	2,543
Interest Income	$ 24	23
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With required reserve recorded, Required Reserve		580
With required reserve recorded, Average Carrying Value Recognized		3,827
With required reserve recorded, Interest Income		6
Carrying Value		2,774
With required reserve recorded, Required Reserve		580
Average Carrying Value Recognized		3,827
Interest Income		$ 6