Business Segment Information - Summary of financial information concerning reportable segments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 1,945,023	$ 1,809,807	$ 1,096,384
Operating profit (loss)	442,390	482,081	238,845
Capital expenditures	328,936	416,400	187,486
Depreciation and amortization	214,899	179,905	133,360
Identifiable assets	1,367,163	1,338,211	887,871
Technical Services
Segment Reporting Information [Line Items]
Revenues	1,794,015	1,663,793	979,834
Operating profit (loss)	420,231	451,259	217,144
Capital expenditures	277,686	369,568	163,362
Depreciation and amortization	183,762	152,252	106,480
Identifiable assets	1,128,124	1,103,341	668,081
Support Services
Segment Reporting Information [Line Items]
Revenues	151,008	146,014	116,550
Operating profit (loss)	45,912	51,672	31,086
Capital expenditures	46,053	42,837	23,012
Depreciation and amortization	30,707	27,464	26,640
Identifiable assets	175,611	177,974	158,577
Corporate
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(17,654)	(17,019)	(13,143)
Capital expenditures	5,197	3,995	1,112
Depreciation and amortization	430	189	240
Identifiable assets	63,428	56,896	61,213
(Loss) Gain on disposition of assets, net
Segment Reporting Information [Line Items]
Revenues
Operating profit (loss)	(6,099)	(3,831)	3,758
Capital expenditures
Depreciation and amortization
Identifiable assets