Investments in Unconsolidated Joint Ventures - Balance Sheet footnotes (Details) - Joint Venture - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total assets	$ 10,054,317		$ 10,054,317		$ 9,944,864
Amortization of difference between cost of investments and book value of underlying equity	5,271	$ 3,524	9,810	$ 7,627
PPR Portfolio
Schedule of Equity Method Investments [Line Items]
Total assets	2,991,383		2,991,383		3,047,851
Total liabilities	$ 1,841,559		$ 1,841,559		$ 1,859,637