SEGMENT REPORTING (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 segment	Jun. 30, 2011	Dec. 31, 2011
Segment reporting information
Third party revenues	$ 523,118	$ 447,235	$ 1,095,140	$ 882,197
Intersegment revenues, net
Direct revenues	523,118	447,235	1,095,140	882,197
Property, plant and equipment, net	955,040		955,040		903,947
Goodwill	135,962		135,962		122,392
Permits and other intangibles, net	138,622		138,622		139,644
Total assets	2,122,214		2,122,214		2,085,803
Reconciliation to Consolidated Statements of Income:
Reporting segments number			4
Number of operations for which the revenues are insignificant			2
Accretion of environmental liabilities	2,505	2,407	4,921	4,796
Depreciation and amortization	38,663	26,936	75,494	52,396
Income from operations	47,533	51,884	109,234	91,626
Other expense (income)	75	(2,868)	374	(5,767)
Interest expense, net of interest income	10,968	10,642	22,240	17,120
Income from continuing operations, before provision for income taxes	36,490	44,110	86,620	80,273
United States
Segment reporting information
Total assets	1,144,546		1,144,546		1,119,491
Canada
Segment reporting information
Total assets	977,668		977,668		961,936
Other foreign
Segment reporting information
Total assets	0		0		4,376
Reportable segments
Segment reporting information
Adjusted EBITDA, Total	88,701	81,227	189,649	148,818
Property, plant and equipment, net	955,040		955,040		903,947
Total Intangible assets	274,584		274,584		262,036
Total assets	2,122,214		2,122,214		2,085,803
Technical Services
Segment reporting information
Third party revenues	229,502	215,747	439,469	411,763
Intersegment revenues, net	7,724	6,901	17,278	10,247
Direct revenues	237,226	222,648	456,747	422,010
Adjusted EBITDA, Total	66,717	63,823	117,542	111,502
Property, plant and equipment, net	311,447		311,447		308,118
Goodwill	45,577		45,577		44,410
Permits and other intangibles, net	80,168		80,168		81,605
Total Intangible assets	125,745		125,745		126,015
Total assets	604,781		604,781		604,904
Field Services
Segment reporting information
Third party revenues	62,553	59,505	114,363	111,196
Intersegment revenues, net	(3,485)	(5,461)	(7,778)	(7,618)
Direct revenues	59,068	54,044	106,585	103,578
Adjusted EBITDA, Total	7,588	8,220	9,892	12,209
Property, plant and equipment, net	34,643		34,643		30,296
Goodwill	2,232		2,232		2,232
Permits and other intangibles, net	1,127		1,127		1,204
Total Intangible assets	3,359		3,359		3,436
Total assets	43,442		43,442		37,850
Industrial Services
Segment reporting information
Third party revenues	149,642	115,013	309,738	227,895
Intersegment revenues, net	(7,835)	(3,567)	(15,371)	(7,046)
Direct revenues	141,807	111,446	294,367	220,849
Adjusted EBITDA, Total	34,935	27,401	69,592	51,697
Property, plant and equipment, net	284,960		284,960		254,469
Goodwill	51,976		51,976		45,444
Permits and other intangibles, net	24,296		24,296		19,701
Total Intangible assets	76,272		76,272		65,145
Total assets	394,180		394,180		345,202
Oil and Gas Field Services
Segment reporting information
Third party revenues	81,091	56,673	230,539	131,007
Intersegment revenues, net	4,118	2,591	6,666	5,391
Direct revenues	85,209	59,264	237,205	136,398
Adjusted EBITDA, Total	7,810	6,974	46,209	20,686
Property, plant and equipment, net	266,709		266,709		267,987
Goodwill	36,177		36,177		30,306
Permits and other intangibles, net	33,031		33,031		37,134
Total Intangible assets	69,208		69,208		67,440
Total assets	371,338		371,338		429,938
Corporate Items
Segment reporting information
Third party revenues	330	297	1,031	336
Intersegment revenues, net	(522)	(464)	(795)	(974)
Direct revenues	(192)	(167)	236	(638)
Adjusted EBITDA, Total	(28,349)	(25,191)	(53,586)	(47,276)
Property, plant and equipment, net	57,281		57,281		43,077
Total assets	$ 708,473		$ 708,473		$ 667,909