Derivatives - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) Derivative
Derivative [Line Items]
Available for sale securities pledged for collateral	$ 487,000		$ 487,000		$ 492,000
Interest expense	$ 8,767,000	$ 5,791,000	16,676,000	$ 11,264,000
Reclassification Out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest expense			$ 371,000
Cash Flow Hedging | Interest Rate Swaps
Derivative [Line Items]
Number of derivatives | Derivative						2
Notional amount						$ 30,000,000
Average interest rate						1.10%
Variable rate basis			3 month LIBOR
Amount of ineffective hedges			$ 0
Cash Flow Hedging | Interest Rate Swaps | Interest Expense
Derivative [Line Items]
Accumulated other comprehensive income (loss) reclassified			$ 132,000	$ (4,000)