Business Segment Information - Summary of financial information concerning reportable segments (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 1,595,227	$ 728,974	$ 1,263,840
Operating profit (loss)	226,217	(238,942)	(156,277)
Capital expenditures	117,509	33,938	167,426
Depreciation and amortization	163,537	217,258	270,977
Identifiable assets	1,147,224	1,035,452	1,237,094
Operating Segments | Technical Services
Segment Reporting Information [Line Items]
Revenues	1,538,351	679,654	1,175,293
Operating profit (loss)	251,476	(203,804)	(132,982)
Capital expenditures	106,131	28,380	155,361
Depreciation and amortization	145,507	191,181	237,778
Identifiable assets	896,803	733,008	976,761
Operating Segments | Support Services
Segment Reporting Information [Line Items]
Revenues	56,876	49,320	88,547
Operating profit (loss)	(12,228)	(26,021)	(2,363)
Capital expenditures	9,949	2,928	11,055
Depreciation and amortization	17,570	25,606	32,697
Identifiable assets	75,568	76,876	108,262
Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0
Operating profit (loss)	(17,561)	(17,037)	(14,515)
Capital expenditures	1,429	2,630	1,010
Depreciation and amortization	460	471	502
Identifiable assets	174,853	225,568	152,071
Gain (loss) on disposition of assets, net
Segment Reporting Information [Line Items]
Revenues	0	0	0
Operating profit (loss)	4,530	7,920	(6,417)
Capital expenditures	0	0	0
Depreciation and amortization	0	0	0
Identifiable assets	$ 0	$ 0	$ 0