Notes and Other Receivables - Allowance for credit loss (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 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	(97)
Ending balance	100
Mezzanine Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0
Impact of adoption ASC 326	100
Provision for credit losses	(47)
Ending balance	100
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	100
Provision for credit losses	(90)
Ending balance	$ 100
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