Other Assets and Deferred Charges, Net (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs And Other Assets [Line Items]
Amortization expense of deferred charges	$ 6.2	$ 5.3	$ 5.2
Unsecured Revolving Credit Facility [Member]
Deferred Costs And Other Assets [Line Items]
Accumulated amortization of deferred lease origination costs	37.1
Accumulated amortization of deferred financing costs	$ 2.1