Leasing Activity (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Tenant reimbursements	$ 19.9	$ 19.8	$ 40.0	$ 40.8
Percentage of leased asset subjected to termination options	4.20%		4.20%
Percentage of leased asset exercisable in period	1.10%		1.10%
Maximum [Member]
Non-cancelable leases term (in years)			10 years
Minimum [Member]
Non-cancelable leases term (in years)			1 year