Debt and Preferred Equity Investments - Roll Forward of Net Book Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Document Period End Date	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 2,099,393	$ 2,114,041
Redemptions/sales/syndications/amortization	(1,190,689)	(994,906)
Net change in loan loss reserves	4,000	(5,750)
Balance at end of period	1,580,306	2,099,393
Debt investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	652,866	834,304
Preferred equity investments
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	$ 14,736	$ 151,704