Impact of Cash Flow Hedges on Results of Operations, Comprehensive Income and Accumulated Other Comprehensive Loss (Detail) (Cash Flow Hedging, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	$ (3,166)	[1]	$ (1,319)	[1]	$ (6,253)	[1]
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	481	[2],[3]	934	[2],[3]	8,050	[2],[3]
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	(4,524)	[1]	(3,224)	[1]	(6,812)	[1]
Fuel Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized as AOCL on Derivatives, Net of Tax (Effective Portion)	1,358	[1]	1,905	[1]	559	[1]
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	3,279	[2],[3]	3,598	[2],[3]	5,612	[2],[3]
Cost Of Operations
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Reclassified from AOCL into Earnings, Net of Tax (Effective portion)	$ (2,798)	[2],[3]	$ (2,664)	[2],[3]	$ 2,438	[2],[3]

[1] In accordance with the derivatives and hedging guidance, the effective portions of the changes in fair values of interest rate swaps and the fuel hedge have been recorded in equity as a component of AOCL. As the critical terms of the interest rate swaps match the underlying debt being hedged, no ineffectiveness is recognized on these swaps and, therefore, all unrealized changes in fair value are recorded in AOCL. Because changes in the actual price of diesel fuel and changes in the DOE index price do not offset exactly each reporting period, the Company assesses whether the fuel hedge is highly effective using the cumulative dollar offset approach.

[2] Amounts reclassified from AOCL into earnings related to realized gains and losses on interest rate swaps are recognized when interest payments or receipts occur related to the swap contracts, which correspond to when interest payments are made on the Company's hedged debt.

[3] Amounts reclassified from AOCL into earnings related to realized gains and losses on the fuel hedge are recognized when settlement payments or receipts occur related to the hedge contract, which correspond to when the underlying fuel is consumed.