Notes Receivable (Schedule of Interest on the Mezzanine Loans) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 5,593	$ 2,375	$ 10,912	$ 4,607
Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	5,571	2,363	10,869	4,585
Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	22	12	43	22
1405 Point | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	173	483	783	936
The Residences at Annapolis Junction | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	2,173	1,124	4,196	2,209
North Decatur Square (a) | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	693	531	1,331	992
Delray Plaza | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	414	225	724	448
Nexton Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	524	0	1,033	0
Interlock Commercial | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1,086	0	1,830	0
Interlock Residential | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 508	$ 0	$ 972	$ 0