Mortgage Loans Payable and Unsecured Credit Facility (Narrative) (Details) - USD ($)			9 Months Ended
	Oct. 29, 2020	Aug. 04, 2020	Sep. 30, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Credit facilities			$ 120,900,000	$ 106,000,000
Approximate amount of accumulated other comprehensive loss to be reclassified into earnings			7,200,000
Interest Rate Swap [Member]
Line Of Credit Facility [Line Items]
Derivative, notional amount			$ 425,000,000.0	$ 425,000,000.0
Unsecured Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 300,000,000
Aggregate borrowing capacity including increase under accordion feature		$ 750,000,000
Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Line of credit facility extension allowed period		1 year	1 year
Basis spread on borrowings variable rate			1.65%
Revolving Credit Facility [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate		1.35%
Revolving Credit Facility [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate		1.95%
Revolving Credit Facility [Member] | Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Credit facility borrowing capacity	$ 44.1
Basis spread on borrowings variable rate	1.65%
Credit facilities	$ 185,000,000.0
Revolving Credit Facility [Member] | Unsecured Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 250,000,000
Credit facility expiration date		Sep. 08, 2021
Term loan facility [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate			1.60%
Term loan facility [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate		1.30%
Term loan facility [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate		1.90%
Term loan facility [Member] | Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Basis spread on borrowings variable rate	1.60%
Term loan facility [Member] | Unsecured Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 50,000,000
Credit facility expiration date		Sep. 08, 2022