Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue	$ 1,921,507	$ 2,271,603	$ 3,062,754
Cost of services and products	1,726,897	1,992,376	2,457,325
Gross Margin	194,610	279,227	605,429
Selling, general and administrative expense	183,954	208,463	231,619
Income from Operations	10,656	70,764	373,810
Interest income	7,355	3,900	607
Interest expense, net of amounts capitalized	(27,817)	(25,318)	(25,050)
Equity earnings of unconsolidated affiliates	(1,983)	244	2,230
Other income (expense), net	(6,055)	(6,244)	(15,336)
Income before Income Taxes	(17,844)	43,346	336,261
Income Tax Expense (Benefit)	(184,242)	18,760	105,250
Net Income	$ 166,398	$ 24,586	$ 231,011
Cash Dividends declared per Share	$ 0.45	$ 0.96	$ 1.08
Basic Earnings per Share	$ 1.69	$ 0.25	$ 2.35
Weighted Average Number of Shares Outstanding, Basic	98,238	98,035	98,417
Diluted Earnings per Share	$ 1.68	$ 0.25	$ 2.34
Weighted Average Number of Shares Outstanding, Diluted	98,764	98,424	98,808
Norway Member
Other income (expense), net		$ (1,100)
Reduction in Taxes [Member]
Income Tax Expense (Benefit)	$ 23,100