BUSINESS ACQUISITIONS (Details)	3 Months Ended								12 Months Ended									12 Months Ended
	Dec. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Jun. 30, 2012 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2011 USD ($)	Jun. 30, 2011 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 Operating Disposal Facilities USD ($)	Dec. 31, 2011 Operating Disposal Facilities USD ($)	Dec. 31, 2010 Operating Disposal Facilities USD ($)	Dec. 31, 2012 Dynecol USD ($) employee	Dec. 31, 2011 Dynecol USD ($)	May 31, 2012 Dynecol USD ($)	Dec. 31, 2012 Dynecol Operating Disposal Facilities	Dec. 31, 2010 Stablex USD ($)	Oct. 31, 2010 Stablex USD ($)	Oct. 31, 2010 Stablex CAD
BUSINESS ACQUISITIONS
Percentage of outstanding shares acquired																	100.00%			100.00%	100.00%
Total post-closing adjustments refund																					1,000,000
Consideration paid and the fair value of assets acquired and liabilities assumed
Current assets																	2,214,000			6,146,000
Property and equipment																	6,552,000			30,470,000
Identifiable intangible assets																	1,940,000			40,978,000
Current liabilities																	(1,268,000)			(6,533,000)
Other liabilities																				(14,839,000)
Total identifiable net assets																	9,438,000			56,222,000
Goodwill																	1,327,000			21,272,000
Total purchase price																	10,765,000			77,494,000	79,000,000
Additional information
Number of employees															40
Number of years for which the acquired entity existed															40 years
Revenue	50,406,000	45,739,000	39,980,000	33,013,000	41,567,000	39,670,000	39,537,000	34,143,000	169,138,000	154,917,000	104,836,000	169,118,000	154,895,000	104,810,000	6,700,000				5,700,000
Operating income	10,814,000	12,393,000	10,960,000	6,471,000	10,403,000	9,567,000	7,754,000	4,641,000	40,638,000	32,365,000	20,377,000	55,005,000	43,983,000	33,266,000	161,000				145,000
Acquisition-related costs included in selling, general and administrative expenses															348,000				2,600,000
Amortization period of goodwill recognized and expected to be deductible for income tax purposes																		15 years
Pro forma combined:
Revenue															174,639,000	169,884,000			133,779,000
Net income															$ 25,513,000	$ 19,339,000			$ 13,547,000
Earnings per share - Basic (in dollars per share)															$ 1.40	$ 1.06			$ 0.75
Earnings per share - Diluted (in dollars per share)															$ 1.40	$ 1.06			$ 0.74