Cash, Cash Equivalents and Restricted Cash (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Restricted cash included in other current assets	$ 17.2		$ 30.3
Restricted cash included in other long-term assets	5.7		6.3
ARO financial assurance [Member]
Restricted cash included in other current assets	17.0		16.6
Increase (decrease) in restricted cash	13.5
Lease turnover financial assurance [Member]
Restricted cash included in other current assets	0.0		13.5
Restricted cash included in other long-term assets			0.0
Workers compensation financial assurance [Member]
Restricted cash included in other current assets	0.0	$ 0.6
Restricted cash included in other long-term assets	$ 5.4		$ 6.0