Securities Available for Sale - Summary of Gross Unrealized Losses on Securities Available-for-sale and Fair Values, Aggregated by Investment category and Length of Time Individual Securities Have Been in a Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 1,143	$ 2,613
Unrealized Loss	(5)	(6)
Fair Value	35,379	56,851
Unrealized Loss	(562)	(2,195)
Fair Value	36,522	59,464
Unrealized Loss	(567)	(2,201)
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value		1,567
Unrealized Loss		(5)
Fair Value	5,018	6,909
Unrealized Loss	(20)	(199)
Fair Value	5,018	8,476
Unrealized Loss	(20)	(204)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	1	29
Fair Value	30,112	49,549
Unrealized Loss	(542)	(1,992)
Fair Value	30,113	49,578
Unrealized Loss	(542)	(1,992)
Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value		204
Fair Value		147
Unrealized Loss		(1)
Fair Value		351
Unrealized Loss		(1)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	893	813
Unrealized Loss	(4)	(1)
Fair Value	893	813
Unrealized Loss	(4)	(1)
Certificates of Deposit [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	249
Unrealized Loss	(1)
Fair Value	249	246
Unrealized Loss		(3)
Fair Value	498	246
Unrealized Loss	$ (1)	$ (3)