Loans and Preferred Equity Held for Investment, net - Changes in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses at beginning of period				$ 272,624	$ 109,328	$ 109,328
Effect of CECL adoption				21,093	0
Provision for loan losses				86,329	220,572
Charge-off				(38,659)	(46,692)
Transfer to loans held for sale				(300,863)	0
Allowance for loan losses at end of period	$ 40,524		$ 283,208	40,524	283,208	$ 272,624
Provision for loan losses transferred to held for sale		$ 5,200
Net impairment				1,800
Provision for loan losses	10,404		$ 110,314	80,285	$ 220,572
Corporate term loans
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses				1,600
PD/LGD model
Allowance for Loan and Lease Losses [Roll Forward]
Unfunded commitments	$ 1,000			1,000
Provision for loan losses				$ 38,900