Derivatives (Details) - Cash Flow Hedging [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized losses on unsettled futures contracts	$ 12.3	$ 7.2
Income tax benefit	(4.5)	(2.6)
Losses included in AOCI, net of tax	7.8	$ 4.6
Cash flow hedge derivative losses expected to be reclassified into earnings within the next 12 months	$ 6.8