Investments in Unconsolidated Joint Ventures - Balance Sheet footnotes (Details) - Joint Venture - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total assets	$ 10,044,705		$ 9,944,864
Amortization of difference between cost of investments and book value of underlying equity	4,539	$ 4,103
PPR Portfolio
Schedule of Equity Method Investments [Line Items]
Total assets	3,023,148		3,047,851
Total liabilities	$ 1,852,923		$ 1,859,637