LONG TERM DEBT AND CAPITAL LEASES - Components of Long-Term Debt and Capital Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 497,680	$ 525,583
Less—unamortized discount and debt issuance costs	15,178	16,936
Long-term debt and capital leases less unamortized discount and debt issuance costs	482,502	508,647
Less—current maturities of long-term debt	4,926	4,686
Long-term debt and capital leases, less current maturities	$ 477,576	503,961
Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate	2.75%
Long-term debt and capital lease	$ 36,000	62,600
Less—unamortized discount and debt issuance costs	3,938	4,965
New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014 due December 2044 - fixed rate interest period through 2019; bearing interest at 3.75%
Debt Instrument [Line Items]
Long-term debt and capital lease	25,000	25,000
Less—unamortized discount and debt issuance costs	$ 1,034	1,221
Debt instrument interest rate	3.75%
New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014R-2 due December 2044 - fixed rate interest period through 2026; bearing interest at 3.125%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 15,000	15,000
Less—unamortized discount and debt issuance costs	$ 511	571
Debt instrument interest rate	3.125%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-3 due January 2025 - fixed rate interest period through 2025; bearing interest at 5.25%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 25,000	0
Less—unamortized discount and debt issuance costs	$ 603	0
Debt instrument interest rate	5.25%
Vermont Economic Development Authority Solid Waste Disposal Long-Term Revenue Bonds Series 2013 due April 2036 - fixed rate interest period through 2018; bearing interest at 4.75%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 15,000	15,000
Less—unamortized discount and debt issuance costs	$ 691	760
Debt instrument interest rate	5.125%
Business Finance Authority of the State of New Hampshire Solid Waste Disposal Revenue Bonds Series 2013 due April 2029 - fixed rate interest period through 2019; bearing interest at 4.00%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 16,000	16,000
Less—unamortized discount and debt issuance costs	$ 573	605
Debt instrument interest rate	4.75%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-2 due January 2025 - fixed rate interest period through 2017; bore interest at 6.25%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 11,000	11,000
Less—unamortized discount and debt issuance costs	$ 436	563
Debt instrument interest rate	4.00%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-2 due January 2025 - fixed rate interest period through 2017; bore interest at 6.25%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 0	21,400
Less—unamortized discount and debt issuance costs	0	$ 502
Debt instrument interest rate		6.25%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-1; letter of credit backed due January 2025 - bore interest at SIFMA Index
Debt Instrument [Line Items]
Long-term debt and capital lease	0	$ 3,600
Less—unamortized discount and debt issuance costs	0	31
Capital leases maturing through September 2023; bearing interest at up to 7.70%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 5,595	5,534
Debt instrument interest rate	7.70%
Notes payable maturing through June 2027; bearing interest at up to 7.00%
Debt Instrument [Line Items]
Long-term debt and capital lease	$ 2,585	449
Debt instrument interest rate	7.00%
Term Loan B Facility due October 2023; bearing interest at LIBOR plus 2.50% | Secured Debt
Debt Instrument [Line Items]
Interest rate	2.50%
Long-term debt and capital lease	$ 346,500	350,000
Less—unamortized discount and debt issuance costs	7,392	7,718
Unamortized discount	$ 1,482	$ 1,712