Fair Value Disclosures - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets transfer between Level 1 and Level 2	$ 0	$ 0	$ 0	$ 0	$ 0
Assets transfer between Level 2 and Level 3	0	0	0	0	0
Impaired loans carrying value	14,129,000	26,695,000	14,129,000	26,695,000	19,714,000
Impaired loans valuation reserves	4,177,000	7,042,000	4,177,000	7,042,000	5,012,000
Impaired loans net fair value	9,952,000		9,952,000
Recorded Investment With No Allowance	4,621,000	7,017,000	4,621,000	7,017,000	7,657,000
Other real estate owned, total	$ 2,176,000	$ 241,000	$ 2,176,000	$ 241,000	$ 413,000
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage			5.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage			25.00%