Fair Value Measurements (Narratives) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Nonrecurring basis | Level 3
Valuation of our interest rate swaps and impaired assets
Impaired long-lived assets	$ 0.4	$ 2.6
Impaired long-lived assets
Valuation of our interest rate swaps and impaired assets
Weighted average disposal period of impaired assets	4 years