Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Accrued insurance		$ 31.1	$ 27.7
Operating loss carryforwards and tax credits		34.9	29.9
Unrealized gains and losses		26.3	10.3
Compensation and benefits		24.1	17.7
Bad debt		4.7	3.1
Other		12.4	13.1
Valuation allowance		(21.4)	(10.6)
Total deferred tax assets	[1]	112.1	91.2
Deferred tax liabilities:
Property and equipment		126.6	118.9
Goodwill		72.8	57.7
Other intangible assets		32.9	37.8
Other		15.3	16.4
Total deferred tax liabilities		278.7	260.8
Net deferred tax liabilities		(166.6)	(169.6)
Gain on Remeasurement of Equity Investee
Deferred tax liabilities:
Deferred income		10.9	11.2
Long-Term Contracts [Member]
Deferred tax liabilities:
Deferred income		$ 20.2	$ 18.8

[1] The table above presents the valuation allowances and related deferred tax assets on a gross basis as of both December 31, 2016 and 2015, whereas in 2015, a portion of the valuation allowances and related deferred tax assets were presented on a net basis.