Derivative Hedging Instruments - Summary of Interest Rate Swap Transactions (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net Exposure, Notional Amount	$ 0	$ 0
Derivative Financial Instruments, Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net Exposure, Notional Amount	$ 60,711,000	$ 52,975,000
Weighted Average Rate Received/(Paid)	5.09%	5.07%
Net Exposure, Impact of a 1 basis point change in interest rates	$ 35,000	$ 30,000
Repricing Frequency	Monthly
Derivative Financial Instruments, Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net Exposure, Notional Amount	$ (60,711,000)	$ (52,975,000)
Weighted Average Rate Received/(Paid)	5.09%	5.07%
Net Exposure, Impact of a 1 basis point change in interest rates	$ (35,000)	$ (30,000)
Repricing Frequency	Monthly