Notes Receivable (Schedule of Interest on the Mezzanine Loans) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 5,710	$ 2,545	$ 16,622	$ 7,152
Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	5,688	2,529	16,557	7,113
Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	22	16	65	39
1405 Point | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	547	783	1,483
The Residences at Annapolis Junction | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	2,340	1,166	6,536	3,374
North Decatur Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	178	569	1,509	1,561
Delray Plaza | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	429	228	1,153	676
Nexton Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	550	19	1,584	19
Interlock Commercial | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1,595	0	3,425	0
Interlock Residential | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	596	$ 0	1,567	$ 0
Annapolis Junction | The Residences at Annapolis Junction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan modification fee	$ 5,000		$ 5,000