Leasing Activity (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating Leased Assets [Line Items]
Rental income, variable lease payments	$ 23.2	$ 24.0	$ 47.8	$ 49.0
Percentage of leased asset subjected to termination options	3.20%		3.20%
Percentage of leased asset exercisable in period	1.90%		1.90%
Termination option, exercisable through date			Dec. 31, 2020
Minimum [Member]
Operating Leased Assets [Line Items]
Non-cancelable lease term	1 year		1 year
Maximum [Member]
Operating Leased Assets [Line Items]
Non-cancelable lease term	10 years		10 years