Real Estate Investments - Preferred Equity Investments and Real Estate Under Development (Details) $ in Thousands	1 Months Ended				12 Months Ended
	Nov. 30, 2018 USD ($)	Oct. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) investment project	Dec. 31, 2017 USD ($) investment	Dec. 31, 2018 investment	Dec. 31, 2018 unit	Dec. 31, 2018 project
Schedule of Equity Method Investments [Line Items]
Co-investment					$ 1,300,140	$ 1,155,984
Commitment to fund preferred equity investment in the project	$ 12,500					$ 153,800
Number of investments with a commitment to fund | investment						8
Annualized preferred return rate	9.90%
Equity method investment, funded amount					$ 151,800
Full redemption of a preferred equity investment		$ 5,000	$ 26,500	$ 2,400
Gain on early redemption of preferred equity investment			$ 1,600
Number of development projects | project					4
Ownership interests, number of active development projects							2		6
Number of units to be developed | unit								1,861
Real Estate predevelopment projects [Member]
Schedule of Equity Method Investments [Line Items]
Actual cost of active development projects					$ 800,000
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Annualized preferred return rate					10.25%	9.50%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Annualized preferred return rate					12.00%	11.30%
Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Commitment to fund preferred equity investment in the project					$ 45,100
Number of investments with a commitment to fund | investment					2
Equity method investment, funded amount					$ 39,600
Total preferred interest investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investment					$ 372,800	$ 265,200