Fair Value Measurements (Adjustments Reclassified from Accumulated Balances Other Comprehensive Income (Loss) to Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Derivative Instruments Gain Loss [Line Items]
Costs of contract revenues	$ 161,294	$ 144,557
Income tax (provision) benefit	(3,285)	(1,389)
Net income (loss)	(11,057)	(8,814)
Fuel Hedge Contracts [Member] | Accumulated Gain Loss Net Cash Flow Hedge Parent [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Derivative Instruments Gain Loss [Line Items]
Costs of contract revenues	(3,319)	(2,041)
Income tax (provision) benefit	(838)	(515)
Net income (loss)	$ (2,481)	$ (1,526)