Notes Receivable and Current Expected Credit Losses (Schedule of Interest on the Mezzanine Loans) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 7,226	$ 5,319
Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	7,203	5,298
Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	23	21
1405 Point | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	610
The Residences at Annapolis Junction | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	2,468	2,024
North Decatur Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	0	638
Delray Plaza | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	489	310
Nexton Square | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	391	510
Interlock Commercial | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	3,017	743
Solis Apartments at Interlock | Mezzanine Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	838	$ 463
Annapolis Junction | The Residences at Annapolis Junction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan modification fee	$ 5,000