Investments in Unconsolidated Joint Ventures - Balance Sheet footnotes (Details) - Joint Venture - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total assets	$ 10,167,175		$ 10,167,175		$ 9,944,864
Amortization of difference between cost of investments and book value of underlying equity	5,354	$ 1,160	15,164	$ 8,787
PPR Portfolio
Schedule of Equity Method Investments [Line Items]
Total assets	2,981,866		2,981,866		3,047,851
Total liabilities	$ 1,836,948		$ 1,836,948		$ 1,859,637