Real Estate - Acquisitions and Conversions - Additional Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Capitalized acquisition costs									$ 300,000
Acquisition costs expensed									2,100,000	$ 2,100,000	$ 8,200,000
Debt assumed									0	0
Net (loss) income	$ (6,671,000)	$ (2,597,000)	$ (2,270,000)	$ (4,160,000)	$ 24,944,000	$ 13,285,000	$ 6,108,000	$ 19,971,000	(15,698,000)	64,308,000	$ 134,592,000
Consolidated Acquisitions And Conversions
Business Acquisition [Line Items]
Revenues									$ 9,000,000	$ 10,200,000
Type of Revenue [Extensible List]									us-gaap:RealEstateMember	us-gaap:RealEstateMember
Net (loss) income									$ 500,000	$ 3,500,000
Core Portfolio
Business Acquisition [Line Items]
Acquisition costs expensed										1,200,000
Fund Portfolio
Business Acquisition [Line Items]
Acquisition costs expensed										$ 900,000