DEBT (Summary of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Short-term Debt [Abstract]
Total short-term debt	$ 0		$ 0		$ 100,000
Long Term Debt
Long-term Debt, Total	2,006,537		2,522,413		2,524,581
Less current maturities	158		170		161
Total long-term debt	2,006,379		2,522,243		2,524,420
Estimated fair value of long-term debt	2,312,178		2,820,399		2,756,202
Line of Credit
Short-term Debt [Abstract]
Total short-term debt	0		0		100,000
10.125% notes due 2015
Long Term Debt
Long-term Debt, Total	151,446	[1]	151,897	[1]	152,317	[1]
6.50% notes due 2016
Long Term Debt
Long-term Debt, Total	127,445	[2]	511,627	[2]	513,369	[2]
6.40% notes due 2017
Long Term Debt
Long-term Debt, Total	218,582	[3]	349,907	[3]	349,897	[3]
7.00% notes due 2018
Long Term Debt
Long-term Debt, Total	399,794	[4]	399,772	[4]	399,751	[4]
10.375% notes due 2018
Long Term Debt
Long-term Debt, Total	248,934	[5]	248,843	[5]	248,757	[5]
7.50% notes due 2021
Long Term Debt
Long-term Debt, Total	600,000	[6]	600,000	[6]	600,000	[6]
7.15% notes due 2037
Long Term Debt
Long-term Debt, Total	239,566	[7]	239,561	[7]	239,557	[7]
Medium-term Notes
Long Term Debt
Long-term Debt, Total	6,000		6,000		6,000
Industrial revenue bonds
Long Term Debt
Long-term Debt, Total	14,000		14,000		14,000
Other Notes
Long Term Debt
Long-term Debt, Total	$ 770		$ 806		$ 933

[1] Includes an increase for the unamortized deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: June 30, 2014 — $1,587 thousand, December 31, 2013 — $2,082 thousand and June 30, 2013 — $2,543 thousand. Additionally, includes decreases for unamortized discounts, as follows: June 30, 2014 — $141 thousand, December 31, 2013 — $185 thousand and June 30, 2013 — $226 thousand. The effective interest rate for these notes is 9.58%.

[2] Includes an increase for the unamortized deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: June 30, 2014 — $2,444 thousand, December 31, 2013 — $11,627 thousand and June 30, 2013 — $13,369 thousand. The effective interest rate for these notes is 6.00%.

[3] Includes decreases for unamortized discounts, as follows: June 30, 2014 — $51 thousand, December 31, 2013 — $93 thousand and June 30, 2013 — $103 thousand. The effective interest rate for these notes is 7.41%.

[4] Includes decreases for unamortized discounts, as follows: June 30, 2014 — $206 thousand, December 31, 2013 — $228 thousand and June 30, 2013 — $249 thousand. The effective interest rate for these notes is 7.87%.

[5] Includes decreases for unamortized discounts, as follows: June 30, 2014 — $1,066 thousand, December 31, 2013 — $1,157 thousand and June 30, 2013 — $1,243 thousand. The effective interest rate for these notes is 10.63%.

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

[7] Includes decreases for unamortized discounts, as follows: June 30, 2014 — $622 thousand, December 31, 2013 — $627 thousand and June 30, 2013 — $631 thousand. The effective interest rate for these notes is 8.05%.