Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) entity	Mar. 31, 2015 USD ($) 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	8		9
Number of REITs in which are included in the operations data | entity	9	10
Balance Sheet Data (unaudited):
Real estate, net	$ 359,005		$ 418,959
Other assets	87,374		101,734
Total liabilities	(159,832)		(203,628)
Shareholders' equity	286,547		$ 317,065
Operating Data (unaudited):
Rental revenues	13,415	$ 13,900
Other revenues	10	2
Operating and maintenance expenses	(7,576)	(8,235)
Depreciation and amortization	(4,510)	(4,975)
Interest expense	(2,197)	(2,457)
Gain on sale, less applicable income tax	19,748
Net income (loss)	$ 18,890	$ (1,765)