Derivative Financial Instruments (Impact of Cash Flow Hedges on Results of Operations, Comprehensive Income and Accumulated Other Comprehensive Loss) (Details) - Cash Flow Hedging [Member] - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized as AOCL on derivatives, net of tax (effective portion)	[1]	$ (4,952)	$ (3,692)
Amount of (gain) or loss reclassified from AOCL into earnings, net of tax (effective portion)	[2],[3]	2,176	1,017
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (gain) or loss reclassified from AOCL into earnings, net of tax (effective portion)	[2],[3]	1,060	638
Cost Of Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (gain) or loss reclassified from AOCL into earnings, net of tax (effective portion)	[2],[3]	1,116	379
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized as AOCL on derivatives, net of tax (effective portion)	[1]	(4,144)	(3,374)
Fuel [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized as AOCL on derivatives, net of tax (effective portion)	[1]	$ (808)	$ (318)

[1] In accordance with the derivatives and hedging guidance, the effective portions of the changes in fair values of interest rate swaps and fuel hedges 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 hedges are 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 hedges are recognized when settlement payments or receipts occur related to the hedge contracts, which correspond to when the underlying fuel is consumed.