LONG-TERM DEBT ADDITIONAL INFORMATION (Details)								3 Months Ended	12 Months Ended
	Oct. 15, 2022	May. 21, 2020	May. 15, 2016	Nov. 15, 2015	Oct. 03, 2012 USD ($)	Nov. 15, 2010 USD ($) $ / shares	Nov. 05, 2010	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Rate	Dec. 31, 2014 USD ($) Rate	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Debt Issuance Costs ($)									$ 974,000	$ 88,000	$ 2,352,000
3.25% Convertible Senior Notes due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date						Nov. 15, 2010
Debt Instrument, Maturity Date			May 15, 2016
Debt Instrument, Interest Rate, Stated Percentage | Rate									3.25%
Debt Instrument, Call Date, Earliest				Nov. 15, 2015
Convertible Senior Note, Shares Issued Upon Conversion									23.5849
Convertible Note Principal Amount						$ 1,000
3.25% Convertible Note, Conversion Price | $ / shares						$ 42.40
3.25% Convertible Debt, Liability Component ($)						$ 94,300,000
3.25% Convertible Debt, Equity Component ($)						$ 20,700,000
3.25% Convertible Debt, Remaining Discount Amortization Period									5 months
Debt Instrument, Interest Rate During Period | Rate									7.40%
Convertible Debt, Interest Expense ($)									$ 3,700,000	3,700,000	3,700,000
Convertible Debt, Amortization of Debt Discount ($)									$ 4,200,000	$ 3,900,000	$ 3,700,000
Debt Instrument, Convertible, If-converted Value in Excess of Principal								$ 29,800,000
7.75% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date					Oct. 03, 2012
Debt Instrument, Maturity Date	Oct. 15, 2022
Debt Instrument, Interest Rate, Stated Percentage | Rate									7.75%
Debt Issuance Costs ($)					$ 11,000,000
Debt Instrument, Call Date, Latest					Oct. 15, 2017
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Initiation Date							Nov. 05, 2010
Line of Credit Facility, Current Borrowing Capacity ($)									$ 450,000,000
Debt agreement Amendment date								Sep. 30, 2015
Line of Credit Facility, Maximum Borrowing Capacity ($)									1,000,000,000
Line of Credit Facility, Expiration Date		May 21, 2020
Line of Credit Facility, Remaining Borrowing Capacity									$ 401,300,000
Credit Facility - Restrictive Covenants									The revolving credit facility contains restrictions as to when we can directly or indirectly, retire, redeem, repurchase or prepay in cash any part of the principal of the 2022 Senior Notes or the Convertible Notes. Among other things, the restriction on redemption of the Convertible Notes requires that immediately after giving effect to any such retirement, redemption, defeasance, repurchase, settlement or prepayment, the aggregate commitment under the revolving credit facility must exceed the aggregate credit exposure under such facility by at least the greater of $115 million or an amount equal to or greater than 30% of such aggregate commitment. The restriction on redemption of the 2022 Senior Notes permits redemption only with the proceeds of issuances of "Permitted Refinancing Indebtedness," which may not exceed $750 million.
Credit Facility - Covenant Description									The revolving credit facility contains covenants customary for agreements of this type, with the most restrictive being certain financial tests on a quarterly basis. The financial tests, as defined per the revolving credit facility, include requirements to: (a) maintain a minimum current ratio of 1.00 to 1.00 and (b) not exceed a maximum leverage ratio of 4.25 to 1.00.
Line of Credit Facility, Increase (Decrease), Net									$ 250,000,000
RNG Credit Facility [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount ($)									$ 11,700,000
First Payment [Member] | 3.25% Convertible Senior Notes due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Frequency of Periodic Payment									May 15
First Payment [Member] | 7.75% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Frequency of Periodic Payment									April 15
Second Payment [Member] | 3.25% Convertible Senior Notes due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Frequency of Periodic Payment									November 15
Second Payment [Member] | 7.75% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Frequency of Periodic Payment									October 15
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate | Rate									2.60%	3.80%
Maximum Borrowing Base [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity ($)									$ 700,000,000