Securities Available for Sale - Summary of Amortized Costs and Fair Values of Securities Available-for-sale, by Contractual Maturity (Detail) $ in Thousands	Sep. 30, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due within one year	$ 1,925
Due within one year through five years	6,150
Due within five years through ten years	3,372
Due after ten years	0
Total	66,875
Due within one year	1,927
Due within one year through five years	6,319
Due within five years through ten years	3,485
Due after ten years	0
Total	69,555
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	51,575
Amortized Cost	53,980
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	3,853
Amortized Cost	$ 3,844

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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