Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) entity	Jun. 30, 2016 USD ($) entity	Dec. 31, 2016 USD ($) entity
Related Party Transactions and Investments in Non-Consolidated Entities
Number of Sponsored REITs the Company held an interest in at period end | entity	6		7
Number of REITs in which are included in the operations data | entity	7	9
Balance Sheet Data (unaudited):
Real estate, net	$ 312,226		$ 345,532
Other assets	77,831		86,594
Total liabilities	(150,971)		(164,820)
Shareholders' equity	239,086		$ 267,306
Operating Data (unaudited):
Rental revenues	28,084	$ 26,681
Other revenues	4	25
Operating and maintenance expenses	(14,466)	(14,497)
Depreciation and amortization	(9,943)	(9,054)
Interest expense	(4,226)	(4,284)
Gain on sale, less applicable income tax		26,397
Net income (loss)	$ (547)	$ 25,268