Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) entity	Jun. 30, 2015 USD ($) entity	Dec. 31, 2015 USD ($) entity
Related Party Transactions and Investments in Non-Consolidated Entities
Number of REITs in which the entity holds non-controlling common stock interest | entity	7		9
Number of REITs in which are included in the operations data | entity	9	10
Balance Sheet Data (unaudited):
Real estate, net	$ 345,499		$ 418,959
Other assets	86,854		101,734
Total liabilities	(160,355)		(203,628)
Shareholders' equity	271,998		$ 317,065
Operating Data (unaudited):
Rental revenues	26,681	$ 28,174
Other revenues	25	25
Operating and maintenance expenses	(14,497)	(15,266)
Depreciation and amortization	(9,054)	(9,925)
Interest expense	(4,284)	(4,930)
Gain on sale, less applicable income tax	26,397
Net income (loss)	$ 25,268	$ (1,922)