Fair Value Measurements and Derivatives - Effects of Fuel Options Which Were Not Designated as Hedging Instruments (Details 4) (Not Designated as Hedging Instrument, Fuel Options, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Not Designated as Hedging Instrument | Fuel Options
Derivative Instruments, Gain (Loss) [Line Items]
Gain recognized in other income (expense)		$ 85