Fair Value Measurements (Narrative) (Details) - Diesel swap gal in Millions	3 Months Ended
Mar. 31, 2017 $ / gal gal
Derivatives, Fair Value [Line Items]
Fixed price swap contract (in gallons) \| gal	6.0
Average contract price (in dollars per gallon)	2.56
Average forward price (in dollars per gallon)	2.60

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration