Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) entity	Sep. 30, 2016 USD ($) 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	$ 311,999		$ 345,532
Other assets	77,140		86,594
Total liabilities	(151,830)		(164,820)
Shareholders' equity	237,309		$ 267,306
Operating Data (unaudited):
Rental revenues	40,775	$ 40,453
Other revenues	5	36
Operating and maintenance expenses	(21,219)	(21,892)
Depreciation and amortization	(14,220)	(13,663)
Interest expense	(6,256)	(6,380)
Gain (loss) on sale, less applicable income tax	(702)	26,397
Net income (loss)	$ (1,617)	$ 24,951