Commitments and Contingencies - Additional Information (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2018 USD ($) ft² Option $ / ft²	Sep. 30, 2018 USD ($) Property	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Property	Sep. 30, 2017 USD ($)	Dec. 31, 2017 Property
Commitments and Contingencies [Line Items]
Rent expense related to operating lease		$ 100,000	$ 200,000	$ 400,000	$ 500,000
Options to renewal of operating lease				false
Operating lease term	7 years
Number of operating lease renewal options | Option	2
Number of operating lease renewal period	5 years
Operating lease estimated commencement date	Dec. 15, 2018
Operating lease rent commencement date	Jan. 01, 2019
Initial annual operating lease base rent due	$ 500,000
Annual escalations in base rent per square foot per year | $ / ft²	0.50
Number of real estate properties leased under operating leases | Property		13		13		15
Number of ground leased properties | Property		5		5
Number of remaining ground leased properties | Property				9
Operating leases future remaining commitments		$ 1,300,000		$ 1,300,000
Number of properties provided for construction financing to tenants | Property				1
Reimbursement to tenants				$ 5,200,000
Number of property for development | Property				3
Purchase between January 1, 2019 and February 11, 2019		8,200,000		$ 8,200,000
Properties secured by the Mortgage tote for purchase | Property				9
Defined contribution plan name				401(k) Plan
Employer matching contribution		14,000	13,000	$ 100,000	100,000
Executive Officers
Commitments and Contingencies [Line Items]
Employment agreement initial term				4 years
Employment agreement automatic extension period upon non-renewal notice not provided				1 year
First 3% of Eligible Compensation
Commitments and Contingencies [Line Items]
Employer matching contribution, percent of match				100.00%
Next 2% of Eligible Compensation
Commitments and Contingencies [Line Items]
Employer matching contribution, percent of match				50.00%
Minimum [Member]
Commitments and Contingencies [Line Items]
Non cancellable remaining lease term				5 months
Maximum
Commitments and Contingencies [Line Items]
Non cancellable remaining lease term				5 years 8 months 12 days
Ground lease renewable term				20 years
New Jersey
Commitments and Contingencies [Line Items]
Area of leased office space | ft²	13,453
General and Administrative Expense
Commitments and Contingencies [Line Items]
Rent expense related to operating lease		$ 100,000	$ 100,000	$ 100,000	$ 100,000