Mortgage Notes Receivable - Allowance for loan loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for Credit Loss, Beginning Balance	$ 10,663	$ 10,590	$ 9,966	$ 4,096
Provision for loan losses (benefits)	280	1,761	4,224	4,432
Charge offs		(1,688)	(696)	(537)
Allowance for Credit Loss, Ending Balance	10,943	10,663	13,494	9,966
Cumulative Effect, Period of Adoption, Adjustment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for Credit Loss, Beginning Balance			$ 1,975
Allowance for Credit Loss, Ending Balance				$ 1,975
Unfunded Loan Commitment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for Credit Loss, Beginning Balance	947
Provision for loan losses (benefits)	(222)	947
Allowance for Credit Loss, Ending Balance	725	947
Funded And Unfunded Loan Commitment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for Credit Loss, Beginning Balance	11,610	10,590
Provision for loan losses (benefits)	58	2,708
Charge offs		(1,688)
Allowance for Credit Loss, Ending Balance	$ 11,668	$ 11,610