Derivative Financial Instruments - Summary of Notional Values and Fair Values of Derivative Financial Instruments (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative assets, at fair value	$ 1,725,000	$ 2,143,000
Derivative liability, at fair value	(595,000)	$ (1,300,000)
Cash Flow Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Derivative asset, notional amount	185,000,000
Derivative liability, notional amount	85,000,000
Derivative assets, at fair value	1,725,000
Derivative liability, at fair value	(595,000)
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.460 % Swap Rate, Expiration Date 05/2020
Derivative [Line Items]
Derivative asset, notional amount	$ 50,000,000
Fixed rate (as a percent)	1.46%
Derivative assets, at fair value	$ 297,000
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.498 % Swap Rate, Expiration Date 05/2021
Derivative [Line Items]
Derivative asset, notional amount	$ 20,000,000
Fixed rate (as a percent)	1.498%
Derivative assets, at fair value	$ 205,000
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.490 % Swap Rate, Expiration Date 05/2021
Derivative [Line Items]
Derivative asset, notional amount	$ 15,000,000
Fixed rate (as a percent)	1.49%
Derivative assets, at fair value	$ 159,000
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.480 % Swap Rate, Expiration Date 05/2021
Derivative [Line Items]
Derivative asset, notional amount	$ 40,000,000
Fixed rate (as a percent)	1.48%
Derivative assets, at fair value	$ 436,000
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.770 % Swap Rate, Expiration Date 03/2023
Derivative [Line Items]
Derivative asset, notional amount	$ 60,000,000
Fixed rate (as a percent)	1.77%
Derivative assets, at fair value	$ 628,000
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 2.048 % Swap Rate, Expiration Date 10/2018
Derivative [Line Items]
Derivative liability, notional amount	$ 30,000,000
Fixed rate (as a percent)	2.048%
Derivative liability, at fair value	$ (178,000)
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.850 % Swap Rate, Expiration Date 10/2018
Derivative [Line Items]
Derivative liability, notional amount	$ 25,000,000
Fixed rate (as a percent)	1.85%
Derivative liability, at fair value	$ (98,000)
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 1.840 % Swap Rate, Expiration Date 10/2018
Derivative [Line Items]
Derivative liability, notional amount	$ 5,000,000
Fixed rate (as a percent)	1.84%
Derivative liability, at fair value	$ (19,000)
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 2.150 % Swap Rate, Expiration Date 05/2020
Derivative [Line Items]
Derivative liability, notional amount	$ 15,000,000
Fixed rate (as a percent)	2.15%
Derivative liability, at fair value	$ (180,000)
Cash Flow Hedging | Designated as Hedging Instrument | Unsecured term loan facility with: 2.150 % Swap Rate, Expiration Date 05/2020
Derivative [Line Items]
Derivative liability, notional amount	$ 10,000,000
Fixed rate (as a percent)	2.15%
Derivative liability, at fair value	$ (120,000)
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Derivative asset, notional amount	125,000,000
Derivative assets, at fair value	$ 1,097,000