DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) MMcf	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) MMcf	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) MMcf	Dec. 31, 2013 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative, Nonmonetary Notional Amount | MMcf	38,100		38,100		16,000
Premiums recorded in other current assets on natural gas contracts held	$ 11,600,000		$ 11,600,000		$ 6,400,000
Fair Value Assets, Transfers between Levels	0	$ 0	0	$ 0
Long-term Debt, including current maturities	1,201,306,000		1,201,306,000		1,201,311,000
Cash and Cash Equivalents, at Carrying Value	52,974,000	$ 59,685,000	52,974,000	$ 59,685,000	11,943,000	$ 3,171,000
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	4,400,000		4,400,000		100,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term Debt, Fair Value	$ 1,200,000,000		$ 1,200,000,000		$ 1,300,000,000