Mortgage Loans Payable and Unsecured Credit Facilities (Summary of the Remaining Unsecured Term Loans) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Amount	$ 175,000,000	$ 106,000,000
Term Loan [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 50,000,000
Maturity date	Feb. 28, 2022
Term Loan [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.90%
Term Loan Two [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 50,000,000
Maturity date	Sep. 30, 2022
Term Loan Two [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan Two [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.90%
Term Loan Three [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 100,000,000
Maturity date	Apr. 30, 2023
Term Loan Three [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.65%
Term Loan Three [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.25%
Term Loan Four [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 75,000,000
Maturity date	Sep. 30, 2024
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.70%
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.25%
Term Loan Five [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 75,000,000
Maturity date	Jul. 31, 2025
Term Loan Five [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.70%
Term Loan Five [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.25%