Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	Jul. 01, 2016 USD ($) a extension	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($) a	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Provision For Doubtful Accounts, Including Straight Line Rent		$ 1,200,000	$ 1,500,000	$ 700,000
Rentable Square Feet		3,372,794	2,129,753
Asset acquisition capitalized acquisition costs		$ 200,000	$ 700,000	300,000
Interest costs capitalized		1,700,000	800,000	42,000
Real estate taxes and insurance costs capitalized		$ 800,000	800,000	100,000
REIT annual taxable income distribution requirement percentage		90.00%
Rents and other receivables		$ 5,565,000	4,938,000
Allowance for doubtful accounts		(2,816,000)	(1,898,000)
Rents and other receivables, net		2,749,000	3,040,000
Deferred rent receivable		11,903,000	7,913,000
Allowance for doubtful accounts		(30,000)	(86,000)
Deferred rent receivable, net		$ 11,873,000	7,827,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Fair value inputs, discount rate		6.00%
Fair Value Inputs, Cap Rate		5.25%
Fair Value Estimate, Property Average Lease Up Period		6 months
Minimum | Building
Summary Of Significant Accounting Policies [Line Items]
Estimated remaining life		10 years
Minimum | Site Improvements
Summary Of Significant Accounting Policies [Line Items]
Estimated remaining life		5 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Fair value inputs, discount rate		8.50%
Fair Value Inputs, Cap Rate		7.50%
Fair Value Estimate, Property Average Lease Up Period		12 months
Maximum | Building
Summary Of Significant Accounting Policies [Line Items]
Estimated remaining life		30 years
Maximum | Site Improvements
Summary Of Significant Accounting Policies [Line Items]
Estimated remaining life		20 years
Construction Employees
Summary Of Significant Accounting Policies [Line Items]
Compensation costs capitalized		$ 1,000,000	900,000	600,000
Leasing Employees
Summary Of Significant Accounting Policies [Line Items]
Compensation costs capitalized		600,000	$ 500,000	$ 500,000
Rancho Cucamonga, CA
Summary Of Significant Accounting Policies [Line Items]
Mortgage Loans on Real Estate, Face Amount of Mortgages	$ 6,000,000	6,000,000
Rentable Square Feet | a	64,965
Proceeds from Fees Received	$ 300,000
Fixed interest rate on notes receivable	10.00%
Financing Receivable, Number Of Extensions | extension	1
Financing Receivable, Extension Term	6 months
Loans and Leases Receivable, Deferred Income	$ 14,000
Mortgage Loans on Real Estate, Carrying Amount of Mortgages		5,900,000
Accrued Investment Income Receivable		84,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums		$ 200,000