LONG TERM DEBT AND CAPITAL LEASES - Fair Value of Debt (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Carrying Value | Revolving Credit Facility due May 2023; bearing interest at LIBOR plus 2.00%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of line of credit	$ 69,600
Carrying Value | Fixed Rate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	121,722
Carrying Value | Secured Debt | Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-2 due August 2035 - fixed rate interest period through 2025; bearing interest at 4.375%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	350,000
Fair Value | Significant Other Observable Inputs (Level 2) | Fixed Rate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	$ 122,000