Notes Receivable and Current Expected Credit Losses (Schedule of Interest on the Mezzanine Loans) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 4,417	$ 5,710	$ 16,055	$ 16,622
Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	4,416	5,688	16,020	16,557
Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1	22	35	65
1405 Point | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	0	0	783
North Decatur Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	178	0	1,509
The Residences at Annapolis Junction | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	2,340	2,468	6,536
Delray Plaza | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	429	489	1,153
Nexton Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	380	550	1,177	1,584
Interlock Commercial | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	3,189	1,595	9,364	3,425
Solis Apartments at Interlock | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	847	$ 596	2,522	$ 1,567
Annapolis Junction | The Residences at Annapolis Junction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan modification fee	$ 5,000		$ 5,000