Intangibles - Additional Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) properties	Jun. 30, 2018 USD ($) properties
Intangibles
Number of properties, held for sale | properties	17	17
Weighted average amortization period for lease intangibles		19 years
Weighted average amortization period for lease intangible liability		20 years
In-place lease intangibles
Intangibles
Finite-lived intangible assets, disposals	$ 0.8	$ 0.9
Impairment of intangible assets, accumulated amortization	0.2	0.3
Impairment of intangible assets	$ (0.6)	$ (0.7)