Debt and Preferred Equity Investments - Rollforward of Total Allowance for Loan Loss Reserves (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Loan loss reserve activity
Balance at beginning of year	$ 1,750	$ 5,750
Current period provision for loan loss	8,403	0
Writeoffs charged against the allowance	0	(4,000)
Balance at end of period	37,957	1,750
Cumulative adjustment upon adoption of ASC 326
Loan loss reserve activity
Balance at beginning of year	$ 27,804	0
Balance at end of period		$ 27,804