Fair Value Disclosures - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets transfer between Level 2 and Level 3	$ 0	$ 0	$ 0
Impaired loans carrying value, recorded investment with allowance	13,793,000	14,661,000
Impaired loans valuation reserves	4,069,000	3,996,000
Impaired loans net fair value	9,724,000
Recorded Investment With No Allowance	13,741,000	3,009,000
Loans held-for-sale at the lower of cost or fair value	2,487,000
Loans held for sale under fair value	19,185,000	0
Other real estate owned, total	448,000	$ 1,347,000
Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale at the lower of cost or fair value	2,487,000
Loans held for sale under fair value	$ 2,594,000
Minimum [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage	5
Maximum [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage	25