Investment Securities - Schedule of Unrealized Loss Positions of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Investment Securities [Line Items]
Available-for-sale securities, Less than 12 Months, Fair Value	$ 4,847,000	$ 56,720,000
Available-for-sale securities, Less than 12 Months, Unrealized Loss	(42,000)	(69,000)
Available-for-sale securities, 12 Months or Longer, Fair Value	6,778,000	8,691,000
Available-for-sale securities, 12 Months or Longer, Unrealized Loss	(163,000)	(201,000)
Available-for-sale securities, Fair Value	11,625,000	65,411,000
Available-for-sale securities, Unrealized Loss	(205,000)	(270,000)
Held-to-maturity securities, Less than 12 Months, Fair Value		537,000
Held-to-maturity securities, Less than 12 Months, Unrealized Loss		(2,000)
Held-to-maturity securities, Fair Value		537,000
Held-to-maturity securities, Unrealized Loss		(2,000)
U.S. Treasury Securities [Member]
Investment Securities [Line Items]
Available-for-sale securities, Less than 12 Months, Fair Value		49,998,000
Available-for-sale securities, Less than 12 Months, Unrealized Loss		(1,000)
Available-for-sale securities, Fair Value		49,998,000
Available-for-sale securities, Unrealized Loss		(1,000)
Collateralized Mortgage Backed [Member]
Investment Securities [Line Items]
Available-for-sale securities, Less than 12 Months, Fair Value	52,000	6,223,000
Available-for-sale securities, Less than 12 Months, Unrealized Loss	(2,000)	(67,000)
Available-for-sale securities, 12 Months or Longer, Fair Value		834,000
Available-for-sale securities, 12 Months or Longer, Unrealized Loss		(1,000)
Available-for-sale securities, Fair Value	52,000	7,057,000
Available-for-sale securities, Unrealized Loss	(2,000)	(68,000)
Municipal Securities [Member]
Investment Securities [Line Items]
Available-for-sale securities, Less than 12 Months, Fair Value	4,296,000
Available-for-sale securities, Less than 12 Months, Unrealized Loss	(39,000)
Available-for-sale securities, Fair Value	4,296,000
Available-for-sale securities, Unrealized Loss	(39,000)
Held-to-maturity securities, Less than 12 Months, Fair Value		537,000
Held-to-maturity securities, Less than 12 Months, Unrealized Loss		(2,000)
Held-to-maturity securities, Fair Value	0	537,000
Held-to-maturity securities, Unrealized Loss		(2,000)
Subordinated Debt [Member]
Investment Securities [Line Items]
Available-for-sale securities, Less than 12 Months, Fair Value	499,000	499,000
Available-for-sale securities, Less than 12 Months, Unrealized Loss	(1,000)	(1,000)
Available-for-sale securities, Fair Value	499,000	499,000
Available-for-sale securities, Unrealized Loss	(1,000)	(1,000)
U.S Government Agencies [Member]
Investment Securities [Line Items]
Available-for-sale securities, 12 Months or Longer, Fair Value	6,778,000	7,857,000
Available-for-sale securities, 12 Months or Longer, Unrealized Loss	(163,000)	(200,000)
Available-for-sale securities, Fair Value	6,778,000	7,857,000
Available-for-sale securities, Unrealized Loss	$ (163,000)	$ (200,000)

Investment Securities [Line Items]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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