Derivatives (Details) - Commodity Price Hedges [Member] - Cash Flow Hedging [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized losses on unsettled futures contracts	$ 5.3	$ 7.2
Income tax benefit	(1.9)	(2.6)
Losses (gains) included in AOCI, net of tax	3.4	$ 4.6
Cash flow hedge derivative gains (losses) expected to be reclassified into earnings within the next 12 months	$ 3.2