Mortgage Notes Payable, Revolving Credit Facility, Interest Expense and Amortization of Deferred Debt Costs - Summary of Notes Payable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Notes Payable [Line Items]
Fixed rate mortgages	$ 897,888	$ 783,400
Interest rate	3.90%	4.25%
Scheduled maturity period	7 years 11 months 6 days
Total notes payable	$ 965,528	$ 907,774
Interest rate during period	5.07%
Fixed rate mortgage notes payable
Notes Payable [Line Items]
Fixed rate mortgages	$ 890,393	844,292
Interest rate	5.25%
Scheduled maturity period	8 years 6 months 26 days
Fixed rate mortgage notes payable | 6.01% due February 2018
Notes Payable [Line Items]
Fixed rate mortgages	$ 0	29,428
Interest rate	6.01%
Fixed rate mortgage notes payable | 5.88% due January 2019
Notes Payable [Line Items]
Fixed rate mortgages	$ 30,201	32,036
Interest rate	5.88%
Fixed rate mortgage notes payable | 5.76% due May 2019
Notes Payable [Line Items]
Fixed rate mortgages	$ 9,783	10,372
Interest rate	5.76%
Fixed rate mortgage notes payable | 5.62% due July 2019
Notes Payable [Line Items]
Fixed rate mortgages	$ 13,529	14,335
Interest rate	5.62%
Fixed rate mortgage notes payable | 5.79% due September 2019
Notes Payable [Line Items]
Fixed rate mortgages	$ 13,543	14,325
Interest rate	5.79%
Fixed rate mortgage notes payable | 5.22% due January 2020
Notes Payable [Line Items]
Fixed rate mortgages	$ 12,029	12,725
Interest rate	5.22%
Fixed rate mortgage notes payable | 5.60% due May 2020
Notes Payable [Line Items]
Fixed rate mortgages	$ 9,948	10,277
Interest rate	5.60%
Fixed rate mortgage notes payable | 5.30% due June 2020
Notes Payable [Line Items]
Fixed rate mortgages	$ 8,244	8,697
Interest rate	5.30%
Fixed rate mortgage notes payable | 5.83% due July 2020
Notes Payable [Line Items]
Fixed rate mortgages	$ 37,998	39,213
Interest rate	5.83%
Fixed rate mortgage notes payable | 5.81% due February 2021
Notes Payable [Line Items]
Fixed rate mortgages	$ 7,325	7,685
Interest rate	5.81%
Fixed rate mortgage notes payable | 6.01% due August 2021
Notes Payable [Line Items]
Fixed rate mortgages	$ 5,649	5,808
Interest rate	6.01%
Fixed rate mortgage notes payable | 5.62% due June 2022
Notes Payable [Line Items]
Fixed rate mortgages	$ 32,673	33,571
Interest rate	5.62%
Fixed rate mortgage notes payable | 6.08% due September 2022
Notes Payable [Line Items]
Fixed rate mortgages	$ 9,999	10,253
Interest rate	6.08%
Fixed rate mortgage notes payable | 6.43% due April 2023
Notes Payable [Line Items]
Fixed rate mortgages	$ 10,877	11,129
Interest rate	6.43%
Fixed rate mortgage notes payable | 6.28% due February 2024
Notes Payable [Line Items]
Fixed rate mortgages	$ 12,577	13,401
Interest rate	6.28%
Fixed rate mortgage notes payable | 7.35% due June 2024
Notes Payable [Line Items]
Fixed rate mortgages	$ 15,452	15,917
Interest rate	7.35%
Fixed rate mortgage notes payable | 7.60% due June 2024
Notes Payable [Line Items]
Fixed rate mortgages	$ 13,438	13,832
Interest rate	7.60%
Fixed rate mortgage notes payable | 7.02% due July 2024
Notes Payable [Line Items]
Fixed rate mortgages	$ 23,873	24,504
Interest rate	7.02%
Fixed rate mortgage notes payable | 7.45% due July 2024
Notes Payable [Line Items]
Fixed rate mortgages	$ 28,115	28,945
Interest rate	7.45%
Fixed rate mortgage notes payable | 7.30% due January 2025
Notes Payable [Line Items]
Fixed rate mortgages	$ 28,025	28,822
Interest rate	7.30%
Fixed rate mortgage notes payable | 6.18% due January 2026
Notes Payable [Line Items]
Fixed rate mortgages	$ 14,537	14,961
Interest rate	6.18%
Fixed rate mortgage notes payable | 5.31% due April 2026
Notes Payable [Line Items]
Fixed rate mortgages	$ 105,817	109,144
Interest rate	5.31%
Fixed rate mortgage notes payable | 4.30% due October 2026
Notes Payable [Line Items]
Fixed rate mortgages	$ 32,016	33,097
Interest rate	4.30%
Fixed rate mortgage notes payable | 4.53% due November 2026
Notes Payable [Line Items]
Fixed rate mortgages	$ 36,507	37,701
Interest rate	4.53%
Fixed rate mortgage notes payable | 4.70% due December 2026
Notes Payable [Line Items]
Fixed rate mortgages	$ 17,086	17,630
Interest rate	4.70%
Fixed rate mortgage notes payable | 5.84% due May 2027
Notes Payable [Line Items]
Fixed rate mortgages	$ 64,472	66,210
Interest rate	5.84%
Fixed rate mortgage notes payable | 4.04% due April 2028
Notes Payable [Line Items]
Fixed rate mortgages	$ 15,859	16,352
Interest rate	4.04%
Fixed rate mortgage notes payable | 3.51% due June 2028
Notes Payable [Line Items]
Fixed rate mortgages	$ 39,968	41,753
Interest rate	3.51%
Fixed rate mortgage notes payable | 3.99% due September 2028
Notes Payable [Line Items]
Fixed rate mortgages	$ 16,055	16,543
Interest rate	3.99%
Fixed rate mortgage notes payable | 3.69% Due March 2030
Notes Payable [Line Items]
Fixed rate mortgages	$ 27,884	28,679
Interest rate	3.69%
Fixed rate mortgage notes payable | 3.99% Due April 2030
Notes Payable [Line Items]
Fixed rate mortgages	$ 14,950	15,357
Interest rate	3.99%
Fixed rate mortgage notes payable | 3.39% due January 2032
Notes Payable [Line Items]
Fixed rate mortgages	$ 39,140	0
Interest rate	3.39%
Fixed rate mortgage notes payable | 4.88% due September 2032
Notes Payable [Line Items]
Fixed rate mortgages	$ 71,211	70,144
Interest rate	4.88%
Fixed rate mortgage notes payable | 3.75% due December 2032
Notes Payable [Line Items]
Fixed rate mortgages	$ 60,000	0
Interest rate	3.75%
Fixed rate mortgage notes payable | 8.00% due April 2034
Notes Payable [Line Items]
Fixed rate mortgages	$ 11,613	11,446
Interest rate	8.00%
Variable rate loans payable
Notes Payable [Line Items]
Variable rate debt	$ 75,135	63,482
Interest rate spread on LIBOR	2.86%
Scheduled maturity period	4 months 8 days
Variable rate loans payable | Revolving credit facility
Notes Payable [Line Items]
Variable rate debt	$ 61,000	49,000
Interest rate spread on LIBOR	1.45%
Variable rate loans payable | Metro Pike Center Bank Loan
Notes Payable [Line Items]
Variable rate debt	$ 14,135	$ 14,482
Interest rate spread on LIBOR	1.65%