Fair Value - Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	$ 28,897	$ 52,690
U.S. Government and Federal Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	24,552	41,559
FNMA Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	1,103	3,606
GNMA Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	3,242	6,809
Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis		500
FHLMC Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis		216
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	28,897	52,690
Level 2 | U.S. Government and Federal Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	24,552	41,559
Level 2 | FNMA Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	1,103	3,606
Level 2 | GNMA Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis	$ 3,242	6,809
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis		500
Level 2 | FHLMC Certificates
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities measure at fair value on recurring basis		$ 216