Fair Value Measurements (Schedule of Balance Sheet Location Fuel Hedge Contracts) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives Fair Value [Line Items]
Fair value hedge liabilities	$ 4,388	$ 3,029
Designated as Hedging Instrument [Member] \| Accrued Liabilities [Member] \| Fuel Hedge Contracts [Member]
Derivatives Fair Value [Line Items]
Fair value hedge liabilities	$ 4,388	$ 3,029

Fair value of all derivative liabilities designated as fair value hedging instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

Name:	us-gaap_FairValueHedgeLiabilitiesAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant