Basis of Presentation New Accounting Rules (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred marketing reimbursement income	$ 0.6		$ 0.3
Marketing reimbursement revenue	0.6	$ 0.7
Property Management Fee Revenue	0.2	0.2
Construction Revenue	$ 0.3	0.1
Prior Period Reclassification Adjustment		$ 0.7
Cost which are not initial direct leasing costs			5.3	$ 5.1
Direct Leasing Commissions Capitalized			$ 0.7	$ 1.0