Notes and Other Receivables - Allowance for credit loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 0
Impact of adoption ASC 326	0
Provision for credit losses	50
Ending balance	66
Mezzanine Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0
Impact of adoption ASC 326	66
Provision for credit losses	(81)
Ending balance	66
Bridge Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0
Impact of adoption ASC 326	0
Provision for credit losses	(43)
Ending balance	0
Mezzanine and Bridge Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0
Impact of adoption ASC 326	66
Provision for credit losses	(124)
Ending balance	$ 66
Cumulative Effect, Period Of Adoption, Adjustment | Mezzanine Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		$ 147
Cumulative Effect, Period Of Adoption, Adjustment | Bridge Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		43
Cumulative Effect, Period Of Adoption, Adjustment | Mezzanine and Bridge Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Impact of adoption ASC 326		$ 190