Derivatives (Narrative) (Details) gal in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Oct. 01, 2016 USD ($)	Dec. 31, 2016 USD ($) gal $ / option	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Net unrealized and realized gains (losses) related to trading portfolio	$ (0.9)		$ 5.7	$ 3.2
Year One [Member]
Derivative [Line Items]
Value of trading portfolio realized		$ 0.2
Diesel Purchases [Member] | Heating Oil [Member]
Derivative [Line Items]
Quantities under derivative contracts | gal		30.7
Average strike price (in dollars per option) | $ / option		1.72
Diesel Purchases [Member] | Minimum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually | gal		45.0
Diesel Purchases [Member] | Maximum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually | gal		50.0
Other Current Liabilities [Member]
Derivative [Line Items]
Right to reclaim cash collateral, liability			$ 1.7
Other Current Assets [Member]
Derivative [Line Items]
Right to reclaim cash collateral, asset		$ 2.8