Available for Sale Securities-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	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 2,613	$ 20,199
Unrealized Loss	(6)	(149)
Fair Value	56,851	42,978
Unrealized Loss	(2,195)	(1,256)
Fair Value	59,464	63,177
Unrealized Loss	(2,201)	(1,405)
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	1,567	1,435
Unrealized Loss	(5)	(18)
Fair Value	6,909	5,866
Unrealized Loss	(199)	(140)
Fair Value	8,476	7,301
Unrealized Loss	(204)	(158)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	29	18,507
Unrealized Loss		(131)
Fair Value	49,549	36,176
Unrealized Loss	(1,992)	(1,104)
Fair Value	49,578	54,683
Unrealized Loss	(1,992)	(1,235)
Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	204	8
Fair Value	147
Unrealized Loss	(1)
Fair Value	351	8
Unrealized Loss	(1)
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	813
Unrealized Loss	(1)
Fair Value		936
Unrealized Loss		(12)
Fair Value	813	936
Unrealized Loss	(1)	(12)
Certificates of Deposit [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value		249
Fair Value	246
Unrealized Loss	(3)
Fair Value	246	$ 249
Unrealized Loss	$ (3)