Business Segment Information - Summary of financial information concerning reportable segments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 2,337,413us-gaap_SalesRevenueNet	$ 1,861,489us-gaap_SalesRevenueNet	$ 1,945,023us-gaap_SalesRevenueNet
Operating profit (loss)	399,970us-gaap_OperatingIncomeLoss	275,413us-gaap_OperatingIncomeLoss	442,390us-gaap_OperatingIncomeLoss
Capital expenditures	371,502	201,681	328,936
Depreciation and amortization	230,813us-gaap_DepreciationAndAmortization	213,128us-gaap_DepreciationAndAmortization	214,899us-gaap_DepreciationAndAmortization
Identifiable assets	1,759,358us-gaap_Assets	1,383,860us-gaap_Assets	1,367,163us-gaap_Assets
Operating Segments \| Technical Services
Segment Reporting Information [Line Items]
Revenues	2,180,457	1,729,732	1,794,015
Operating profit (loss)	390,004	276,246	420,231
Capital expenditures	342,932	167,586	277,686
Depreciation and amortization	198,636	181,026	183,762
Identifiable assets	1,514,084	1,113,877	1,128,124
Operating Segments \| Support Services
Segment Reporting Information [Line Items]
Revenues	156,956	131,757	151,008
Operating profit (loss)	42,510	26,223	45,912
Capital expenditures	27,148	32,250	46,053
Depreciation and amortization	31,578	31,417	30,707
Identifiable assets	157,688	202,243	175,611
Corporate
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(17,072)	(17,685)	(17,654)
Capital expenditures	1,422	1,845	5,197
Depreciation and amortization	599	685	430
Identifiable assets	87,586	67,740	63,428
Loss on disposition of assets, net
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(15,472)	(9,371)	(6,099)
Capital expenditures
Depreciation and amortization
Identifiable assets

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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