Mortgage Loans Payable and Credit Facility (Summary of Amended and Restated Terms of Existing Unsecured Term Loans) (Details) - USD ($)	Sep. 08, 2017	Sep. 30, 2017	Dec. 31, 2016
Line Of Credit Facility [Line Items]
Amount		$ 95,000,000	$ 72,000,000
Term Loan Two [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 75,000,000
Maturity date	Feb. 28, 2021
Term Loan Two [Member] | Unsecured Term Loans [Member] | Previously [Member]
Line Of Credit Facility [Line Items]
Maturity date	Feb. 28, 2021
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 Two [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.70%
Term Loan Two [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.30%
Term Loan Three [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 50,000,000
Maturity date	Feb. 28, 2022
Term Loan Three [Member] | Unsecured Term Loans [Member] | Previously [Member]
Line Of Credit Facility [Line Items]
Maturity date	Feb. 28, 2022
Term Loan Three [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan Three [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] | LIBOR [Member] | Previously [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.55%
Term Loan Three [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.15%
Term Loan Four [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 50,000,000
Maturity date	Sep. 30, 2022
Term Loan Four [Member] | Unsecured Term Loans [Member] | Previously [Member]
Line Of Credit Facility [Line Items]
Maturity date	Feb. 29, 2020
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.90%
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan Four [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.90%
Term Loan Six [Member] | Unsecured Term Loans [Member]
Line Of Credit Facility [Line Items]
Amount	$ 75,000,000
Maturity date	Sep. 30, 2024
Term Loan Six [Member] | Unsecured Term Loans [Member] | Previously [Member]
Line Of Credit Facility [Line Items]
Maturity date	Feb. 28, 2019
Term Loan Six [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.70%
Term Loan Six [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	2.25%
Term Loan Six [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.30%
Term Loan Six [Member] | Unsecured Term Loans [Member] | LIBOR [Member] | Previously [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Interest range	1.90%