Revenues - Summary of Amount Receivable from Customers under Various Fee Agreement (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	$ 17,082
Balance as of June 30, 2018	15,549
Revenue from Contract with Customers Under Various Fee Agreements [Member]
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	1,558
Balance as of June 30, 2018	1,651
Increase (decrease)	93
Revenue from Contract with Customers Under Various Fee Agreements [Member] | Property Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	290
Balance as of June 30, 2018	274
Increase (decrease)	(16)
Revenue from Contract with Customers Under Various Fee Agreements [Member] | Asset Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	762
Balance as of June 30, 2018	836
Increase (decrease)	74
Revenue from Contract with Customers Under Various Fee Agreements [Member] | Acquisition, Disposition and Leasing Fee [Member]
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	490
Balance as of June 30, 2018	490
Revenue from Contract with Customers Under Various Fee Agreements [Member] | Other Fee Income [Member]
Disaggregation Of Revenue [Line Items]
Balance as of December 31, 2017	16
Balance as of June 30, 2018	51
Increase (decrease)	$ 35