Basis of Presentation and Significant Accounting Policies - Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ 542,208	$ 416,454
Cost of operations	(392,443)	(303,635)
Income before Provision for Income Taxes	98,448	62,877
Provision for Income Taxes	(22,828)	(13,767)
Other – net	7,917	7,521
Net Income	75,620	49,110
Accumulated Other Comprehensive Income (Loss) Component Recognized
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(1,030)	(370)
Accumulated Other Comprehensive Income (Loss) Component Recognized | Realized gain (loss) on derivative financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	(1)	(12)
Cost of operations	(557)	202
Income before Provision for Income Taxes	(558)	190
Provision for Income Taxes	138	(49)
Net Income	(420)	141
Accumulated Other Comprehensive Income (Loss) Component Recognized | Amortization of prior service cost on benefit obligations
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Taxes	167	136
Other – net	(777)	(647)
Net Income	$ (610)	$ (511)