Business Segment Information - Summary of financial information concerning reportable segments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 1,861,489	$ 1,945,023	$ 1,809,807
Operating profit (loss)	275,413	442,390	482,081
Capital expenditures	201,681	328,936	416,400
Depreciation and amortization	213,128	214,899	179,905
Identifiable assets	1,383,860	1,367,163	1,338,211
Operating Segments | Technical Services
Segment Reporting Information [Line Items]
Revenues	1,729,732	1,794,015	1,663,793
Operating profit (loss)	276,246	420,231	451,259
Capital expenditures	167,586	277,686	369,568
Depreciation and amortization	181,026	183,762	152,252
Identifiable assets	1,113,877	1,128,124	1,103,341
Operating Segments | Support Services
Segment Reporting Information [Line Items]
Revenues	131,757	151,008	146,014
Operating profit (loss)	26,223	45,912	51,672
Capital expenditures	32,250	46,053	42,837
Depreciation and amortization	31,417	30,707	27,464
Identifiable assets	202,243	175,611	177,974
Corporate
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(17,685)	(17,654)	(17,019)
Capital expenditures	1,845	5,197	3,995
Depreciation and amortization	685	430	189
Identifiable assets	67,740	63,428	56,896
Loss on disposition of assets, net
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(9,371)	(6,099)	(3,831)
Capital expenditures
Depreciation and amortization
Identifiable assets