LONG-TERM DEBT - Summary of Components of Long-Term Debt and Capital Leases by Debt Instrument (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 536,772	$ 555,249
Finance leases maturing through December 2107; bearing interest at a weighted average of 5.2%	16,510
Less - unamortized debt issuance costs	9,226	10,950
Long-term debt and finance leases less unamortized debt issuance costs	527,546	544,299
Less—current maturities of long-term debt and finance leases	3,571	2,298
Long-term debt and finance leases, less current portion	$ 523,975	$ 542,001
Weighted-average discount rate - finance leases	5.20%	5.20%
Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.75%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 43,400	$ 69,600
Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.75% \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%	1.75%
Secured Debt \| Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.75%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 350,000	$ 350,000
Secured Debt \| Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.75% \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%	1.75%
Credit Facility
Debt Instrument [Line Items]
Less - unamortized debt issuance costs	$ 5,889	$ 7,118
New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014 ("New York Bonds 2014") due December 2044 - fixed rate interest period through 2019; bearing interest at 3.75%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	25,000	25,000
Less - unamortized debt issuance costs	$ 707	$ 847
Stated interest rate	3.75%	3.75%
New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014R-2 ("New York Bonds 2014R-2") due December 2044 - fixed rate interest period through 2026; bearing interest at 3.125%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 15,000	$ 15,000
Less - unamortized debt issuance costs	$ 405	$ 450
Stated interest rate	3.125%	3.125%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-3 ("FAME Bonds 2005R-3") due January 2025 - fixed rate interest period through 2025; bearing interest at 5.25%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 25,000	$ 25,000
Less - unamortized debt issuance costs	$ 453	$ 517
Stated interest rate	5.25%	5.25%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-1 ("FAME Bonds 2015R-1") due August 2035 - fixed rate interest period through 2025; bearing interest at 5.125%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 15,000	$ 15,000
Less - unamortized debt issuance costs	$ 569	$ 622
Stated interest rate	5.125%	5.125%
Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-2 ("FAME Bonds 2015R-2") due August 2035 - fixed rate interest period through 2025; bearing interest at 4.375%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 15,000	$ 15,000
Less - unamortized debt issuance costs	$ 436	$ 493
Stated interest rate	4.375%	4.375%
Vermont Economic Development Authority Solid Waste Disposal Long-Term Revenue Bonds Series 2013 ("Vermont Bonds") due April 2036 - fixed rate interest period through 2028; bearing interest at 4.625%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 16,000	$ 16,000
Less - unamortized debt issuance costs	$ 554	$ 595
Stated interest rate	4.625%	4.625%
Business Finance Authority of the State of New Hampshire Solid Waste Disposal Revenue Bonds Series 2013 ("New Hampshire Bonds") due April 2029 - fixed rate interest period through September 2019; bore interest at 4.00%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 11,000	$ 11,000
Less - unamortized debt issuance costs	$ 213	$ 308
Stated interest rate	4.00%	4.00%
Finance leases maturing through December 2107; bearing interest at a weighted average of 5.2%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases		$ 11,248
Notes payable maturing through June 2027; bearing interest at a weighted average of 3.5%
Debt Instrument [Line Items]
Principal amount of long-term debt and finance leases	$ 4,862	$ 2,401
Weighted average interest rate	3.50%	3.50%

Amount of short-term and long-term debt and lease obligation.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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