Notes Receivable and Current Expected Credit Losses (Schedule of Interest on the Mezzanine Loans) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 4,412	$ 5,593	$ 11,638	$ 10,912
Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	4,400	5,571	11,604	10,869
Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	12	22	34	43
1405 Point | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	173	0	783
North Decatur Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	693	0	1,331
The Residences at Annapolis Junction | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	2,173	2,468	4,196
Delray Plaza | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	414	489	724
Nexton Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	405	524	797	1,033
Interlock Commercial | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	3,157	1,086	6,175	1,830
Solis Apartments at Interlock | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	838	$ 508	1,675	$ 972
Annapolis Junction | The Residences at Annapolis Junction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan modification fee	$ 5,000		$ 5,000