Acquired Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Above- Market and Below- Market Leases [Member] | Operating Income [Member]
Business Acquisition [Line Items]
Amortization from acquired leases	$ 1,791,000	$ 1,833,000	$ 1,426,000
Above- Market and Below- Market Leases [Member] | Operating Expense [Member]
Business Acquisition [Line Items]
Amortization from acquired leases	320,000	333,000	333,000
Above- Market and Below- Market Leases [Member] | Prepaid Expenses And Other Assets [Member]
Business Acquisition [Line Items]
Finite lived intangible asset	3,189,000	2,527,000
Accumulated amortization	4,698,000	4,210,000
Above- Market and Below- Market Leases [Member] | Accounts Payable and Accrued Liabilities [Member]
Business Acquisition [Line Items]
Accumulated amortization	15,578,000	13,619,000
Finite lived intangible liabilities	22,714,000	22,539,000
In-Place Leases [Member]
Business Acquisition [Line Items]
Depreciation and amortization expense	1,855,000	1,395,000	$ 1,019,000
In-Place Leases [Member] | Prepaid Expenses And Other Assets [Member]
Business Acquisition [Line Items]
Finite lived intangible asset	35,704,000	20,984,000
Accumulated amortization	$ 7,043,000	$ 5,187,000