DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) MMcf	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) MMcf	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) MMcf	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative, Nonmonetary Notional Amount | MMcf	30,500		30,500		17,000
Premiums recorded in other current assets on natural gas contracts held	$ 9,400,000		$ 9,400,000		$ 5,800,000
Fair Value Assets, Transfers between Levels	0	$ 0	0	$ 0
Long-term Debt, including current maturities	1,192,248,000		1,192,248,000		1,191,660,000
Cash and Cash Equivalents, at Carrying Value	4,513,000	$ 52,974,000	4,513,000	$ 52,974,000	2,433,000	$ 11,943,000
Long-term Debt	1,200,000,000		1,200,000,000		1,200,000,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value, natural gas call options	8,100,000		8,100,000		400,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term Debt, Fair Value	$ 1,300,000,000		$ 1,300,000,000		$ 1,200,000,000