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	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 10,203	$ 2,613
Unrealized Loss	(34)	(6)
Fair Value	20,182	56,851
Unrealized Loss	(177)	(2,195)
Fair Value	30,385	59,464
Unrealized Loss	(211)	(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	2,028	6,909
Unrealized Loss	(7)	(199)
Fair Value	2,028	8,476
Unrealized Loss	(7)	(204)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	9,362	29
Unrealized Loss	(33)
Fair Value	18,154	49,549
Unrealized Loss	(170)	(1,992)
Fair Value	27,516	49,578
Unrealized Loss	(203)	(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	841	813
Unrealized Loss	(1)	(1)
Fair Value	841	813
Unrealized Loss	$ (1)	(1)
Certificates of Deposit [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value		246
Unrealized Loss		(3)
Fair Value		246
Unrealized Loss		$ (3)