Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Derivative Financial Instruments (Textual) [Abstract]
Number of interest rate swap agreements	3
Number of fuel hedge agreements	1
Cash Flow Hedging [Member]
Summary of Cash Flow Hedges on results of operations, comprehensive income and accumulated other comprehensive loss
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	$ 290	$ 2,923
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	8	654
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Summary of Cash Flow Hedges on results of operations, comprehensive income and accumulated other comprehensive loss
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	(623)	41
Interest Rate Swap [Member] | Interest Expense [Member]
Summary of Cash Flow Hedges on results of operations, comprehensive income and accumulated other comprehensive loss
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	708	1,157
Fuel Hedges [Member]
Summary of Cash Flow Hedges on results of operations, comprehensive income and accumulated other comprehensive loss
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	913	2,882
Fuel Hedges [Member] | Cost of Operations [Member]
Summary of Cash Flow Hedges on results of operations, comprehensive income and accumulated other comprehensive loss
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	$ (700)	$ (503)