Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) entity	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) entity	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) entity	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of Sponsored REITs the Company held an interest in at period end | entity	2								2		3
Number of REITs in which are included in the operations data | entity											6
Balance Sheet Data (unaudited):
Real Estate Investment Property, Net	$ 1,602,016				$ 1,637,210				$ 1,602,016	$ 1,637,210
Total liabilities	(1,025,093)				(1,056,258)				(1,025,093)	(1,056,258)
Total stockholders' equity	768,091				786,396				768,091	786,396	$ 837,634	$ 871,292
Operating Data (unaudited):
Rental revenues											263,777
Other revenues	59,810	$ 62,247	$ 60,808	$ 62,983	68,997	$ 68,539	$ 66,813	$ 64,716
Depreciation and amortization									(91,581)	(93,787)	(97,171)
Interest expense									(36,026)	(36,757)	(38,374)
Net income	$ 37,440	$ (1,679)	$ (2,075)	$ (1,071)	$ 3,648	$ 2,399	$ 1,633	$ (1,205)	32,615	6,475	13,069
Sponsored REITs
Balance Sheet Data (unaudited):
Real Estate Investment Property, Net											97,034
Other assets											18,532
Total liabilities											(75,382)
Total stockholders' equity											40,184
Operating Data (unaudited):
Rental revenues											40,382
Operating and maintenance expenses											(20,584)
Depreciation and amortization											(13,077)
Interest expense											(6,869)
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes											17,095
Net income											16,948
Related party revenue: Other
Operating Data (unaudited):
Other revenues									$ 31	$ 21	32
Related party revenue: Other | Sponsored REITs
Operating Data (unaudited):
Other revenues											$ 1