Commitments and Contingencies (Detail) a in Thousands, ft² in Millions		3 Months Ended		6 Months Ended
	Sep. 14, 2016 a	Jun. 30, 2017 USD ($) ft² tenant	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) ft²	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Feb. 25, 2014 USD ($)
Commitments And Contingencies [Line Items]
Estimated remediation, processing and oversight costs							$ 1,300,000
Holdback Escrow total funded							1,400,000
Holdback Escrow seller funded							1,300,000
Holdback Escrow buyer funded							100,000
Maximum seller liability remediation costs							$ 1,300,000.0
Contingent liability		$ 1,100,000		$ 1,100,000		$ 1,100,000
Indemnification asset		$ 1,100,000		$ 1,100,000		$ 1,100,000
Ground lease, expiration date		Jun. 01, 2062
Area of real estate property (square feet) | ft²		16.2		16.2
Other commitments		$ 11,900,000		$ 11,900,000
Cash, FDIC Insured Amount		$ 250,000		250,000
Customer Concentration Risk | Base Rent
Commitments And Contingencies [Line Items]
Number of major tenants | tenant		0
Customer Concentration Risk | Total Rental Revenues
Commitments And Contingencies [Line Items]
Concentration risk, percentage		5.00%
Ground Lease
Commitments And Contingencies [Line Items]
Rent expense		$ 36,000	$ 36,000	100,000	$ 100,000
Ground Lease | Corona, CA
Commitments And Contingencies [Line Items]
Area of real estate property (square feet) | a	1,580
Contingency period	420 days
Corona Lease Transaction Costs		300,000
Office Leases
Commitments And Contingencies [Line Items]
Rent expense		$ 100,000	$ 100,000	$ 200,000	$ 300,000