Fair Value Measurements (Adjustments Reclassified From Accumulated Balances Other Comprehensive Loss To Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments Gain Loss [Line Items]
Costs of contract revenues	$ (178,824)	$ (196,717)	$ (489,889)	$ (567,182)
Income tax (provision) benefit	2,850	742	(559)	(2,831)
Net income (loss)	(4,560)	$ (312)	1,194	$ 5,354
Fuel Hedge Contracts [Member] | Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges | Reclassification Out Of Accumulated Other Comprehensive Income
Derivative Instruments Gain Loss [Line Items]
Costs of contract revenues	76		76
Income tax (provision) benefit	30		30
Net income (loss)	$ 46		$ 46