DEBT (Summary of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Long Term Debt
Total long-term debt including current maturities	$ 2,277,896		$ 2,005,584		$ 2,006,953
Less current maturities	365,441	[1]	150,137	[1]	171	[1]
Total long-term debt	1,912,455		1,855,447		2,006,782
Estimated fair value of long-term debt	2,160,255		2,113,478		2,313,964
10.125% notes due 2015 [Member]
Long Term Debt
Total long-term debt including current maturities	150,728	[1],[2]	150,973	[1],[2]	151,674	[1],[2]
6.50% notes due 2016 [Member]
Long Term Debt
Total long-term debt including current maturities	126,725	[3],[4]	126,969	[3],[4]	127,678	[3],[4]
6.40% notes due 2017 [Member]
Long Term Debt
Total long-term debt including current maturities	218,592	[3],[5]	218,589	[3],[5]	218,578	[3],[5]
7.00% notes due 2018 [Member]
Long Term Debt
Total long-term debt including current maturities	272,580	[6]	399,816	[6]	399,783	[6]
10.375% notes due 2018 [Member]
Long Term Debt
Total long-term debt including current maturities	249,080	[7]	249,030	[7]	248,888	[7]
7.50% notes due 2021 [Member]
Long Term Debt
Total long-term debt including current maturities	600,000	[8]	600,000	[8]	600,000	[8]
8.85% notes due 2021 [Member]
Long Term Debt
Total long-term debt including current maturities	6,000	[3],[9]	6,000	[3],[9]	6,000	[3],[9]
Industrial revenue bonds [Member]
Long Term Debt
Total long-term debt including current maturities	14,000	[10],[3]	14,000	[10],[3]	14,000	[10],[3]
4.50% notes due 2025 [Member]
Long Term Debt
Total long-term debt including current maturities	400,000	[11]	0	[11]	0	[11]
7.15% notes due 2037 [Member]
Long Term Debt
Total long-term debt including current maturities	239,573	[12]	239,570	[12]	239,564	[12]
Other Notes
Long Term Debt
Total long-term debt including current maturities	$ 618	[13]	$ 637	[13]	$ 788	[13]

[1] The 10.125% notes due 2015 are classified as long-term debt (not current maturities) as of March 31, 2015 due to our intent and ability to refinance these notes at maturity using our line of credit.

[2] Includes an increase for the unamortized deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: March 31, 2015 — $799 thousand, December 31, 2014 — $1,068 thousand and March 31, 2014 — $1,837 thousand. Additionally, includes decreases for unamortized discounts, as follows: March 31, 2015 — $71 thousand, December 31, 2014 — $95 thousand and March 31, 2014 — $163 thousand. The effective interest rate for these notes is 9.575%.

[3] As of March 31, 2015, we had initiated prepayment, or announced our intent to prepay; as such, this debt is classified as current maturities of long-term debt.

[4] Includes an increase for the unamortized deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: March 31, 2015 — $1,724 thousand, December 31, 2014 — $1,968 thousand and March 31, 2014 — $2,677 thousand. The effective interest rate for these notes is 6.00%.

[5] Includes decreases for unamortized discounts, as follows: March 31, 2015 — $41 thousand, December 31, 2014 — $44 thousand and March 31, 2014 — $55 thousand. The effective interest rate for these notes is 7.39%.

[6] Includes decreases for unamortized discounts, as follows: March 31, 2015 — $117 thousand, December 31, 2014 — $184 thousand and March 31, 2014 — $217 thousand. The effective interest rate for these notes is 7.87%.

[7] Includes decreases for unamortized discounts, as follows: March 31, 2015 — $920 thousand, December 31, 2014 — $970 thousand and March 31, 2014 — $1,112 thousand. The effective interest rate for these notes is 10.625%.

[8] The effective interest rate for these notes is 7.75%.

[9] The effective interest rate for these notes is 8.88%.

[10] This variable-rate tax-exempt bond is backed by a letter of credit.

[11] The effective interest rate for these notes is 4.65%.

[12] Includes decreases for unamortized discounts, as follows: March 31, 2015 — $615 thousand, December 31, 2014 — $618 thousand and March 31, 2014 — $624 thousand. The effective interest rate for these notes is 8.05%.

[13] Non-publicly traded debt.