BUSINESS COMBINATIONS (Assets Aquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2015	Apr. 11, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Measurement period adjustments, accounts receivable	$ (444)
Measurement period adjustment, inventories and supplies	0
Measurement period adjustment, prepaid and other current assets	8
Measurement period adjustments, property, plant and equipment	(1,606)
Measurement period adjustments, permits and other intangibles	(1,500)
Measurement period adjustments, current liabilities	0
Measurement period adjustments, closure and post-closure liabilities	0
Measurement period adjustments, deferred taxes, unrecognized tax benefits and other long-term liabilities	1,832
Measurement period adjustments, total identifiable net assets	(1,710)
Goodwill	447,918		$ 452,669
Measurement period adjustments, goodwill	1,710
Measurement period adjustments, total	0
Thermo Fluids Inc. [Member]
Business Acquisition [Line Items]
Accounts receivable	6,665	$ 7,109
Inventories and supplies	1,791	1,791
Prepaid and other current assets	1,757	1,749
Property, plant and equipment	28,862	30,468
Permits and other intangibles	18,500	20,000
Current liabilities	(5,859)	(5,859)
Closure and post-closure liabilities	(1,676)	(1,676)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(11,249)	(13,081)
Total identifiable net assets	38,791	40,501
Goodwill	38,301	36,591
Total	$ 77,092	$ 77,092