Related Party Transactions and Investments in Non-Consolidated Entities - Investment in Sponsored REITs (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2017 entity property	Dec. 31, 2016 entity property
Related Party Transactions and Investments in Non-Consolidated Entities
Number of REITs in which the entity holds non-controlling common stock interest | entity	6	7
Number of REITs in which the entity holds non-controlling preferred stock interest | entity	2
Number of properties sold | property	1	2
Number of entities holding mortgage loans | property	2	2