BUSINESS SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues
Revenues	$ 472,418	$ 502,235	$ 1,475,081	$ 1,327,025
Operating profit:
Loss on disposition of assets, net	(1,551)	(4,179)	(4,859)	(2,690)
Operating profit	102,368	134,454	353,083	360,047
Interest expense	(441)	(887)	(1,687)	(2,964)
Interest income	16	9	25	16
Other income (expense), net	1,104	(906)	1,144	(582)
Income before income taxes	103,047	132,670	352,565	356,517
Identifiable assets at September 30, 2012	1,358,146		1,358,146
Capital expenditures			273,801	305,729
Depreciation and amortization	54,082	46,476	159,602	130,906
Technical Services
Revenues
Revenues	436,056	463,685	1,359,220	1,219,823
Operating profit:
Operating profit	98,708	127,877	334,610	337,302
Identifiable assets at September 30, 2012	1,119,339		1,119,339
Capital expenditures			230,110
Depreciation and amortization			136,387
Support Services
Revenues
Revenues	36,362	38,550	115,861	107,202
Operating profit:
Operating profit	10,004	14,121	36,532	37,210
Identifiable assets at September 30, 2012	187,418		187,418
Capital expenditures			40,668
Depreciation and amortization			22,918
Corporate
Operating profit:
Operating profit	(4,793)	(3,365)	(13,200)	(11,775)
Identifiable assets at September 30, 2012	51,389		51,389
Capital expenditures			3,023
Depreciation and amortization			$ 297