Recent Accounting Standards Recent Accounting Standards (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Postretirement costs	$ 4.8	$ 0.8	$ 6.4	$ 2.4
Restricted cash	$ 3.1	$ 3.9	$ 3.1	$ 3.9	$ 2.5	$ 3.2