DEBT (Summary of Debt) (Details) - USD ($)		Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Debt Instrument [Line Items]
Total short-term debt		$ 0	$ 0	$ 138,500,000
Total long-term debt including current maturities		1,982,658,000	1,980,464,000	1,907,861,000
Unamortized discounts and debt issuance costs		(21,531,000)	(23,734,000)	(25,975,000)
Less current maturities		131,000	130,000	14,124,000
Total long-term debt		1,982,527,000	1,980,334,000	1,893,737,000
Total debt	[1]	1,982,658,000	1,980,464,000	2,046,361,000
Estimated fair value of long-term debt		2,272,149,000	2,204,816,000	2,140,942,000
10.125% notes due 2015 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		0	0	150,000,000
6.50% notes due 2016 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		0	0	0
6.40% notes due 2017 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		0	0	0
7.00% notes due 2018 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		272,512,000	272,512,000	272,512,000
10.375% notes due 2018 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		250,000,000	250,000,000	250,000,000
7.50% notes due 2021 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		600,000,000	600,000,000	600,000,000
8.85% notes due 2021 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		6,000,000	6,000,000	6,000,000
4.50% notes due 2025 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		400,000,000	400,000,000	400,000,000
7.15% notes due 2037 [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		240,188,000	240,188,000	240,188,000
10.125% notes due 2015 and 6.50% notes due 2016 [Member]
Debt Instrument [Line Items]
Unamortized deferred interest rate swap gain	[2]	0	0	523,000
Bank Line of Credit [Member]
Debt Instrument [Line Items]
Total short-term debt	[3],[4],[5]	0	0	138,500,000
Bank Line of Credit [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities	[3],[4],[5]	235,000,000	235,000,000	0
Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities		0	0	14,000,000
Other Notes [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities	[4]	$ 489,000	$ 498,000	$ 613,000

[1] Face value of our debt is equal to total debt less unamortized discounts and debt issuance costs, and unamortized deferred interest rate swap gain, as follows: June 30, 2016 - $2,004,189 thousand, December 31, 2015 - $2,004,198 thousand and June 30, 2015 - $2,071,813 thousand.

[2] The unamortized deferred gain was realized upon the August 2011 settlement of interest rate swaps as described in Note 6.

[3] Borrowings on the bank line of credit are classified as short-term debt if we intend to repay within twelve months and as long-term debt otherwise.

[4] Non-publicly traded debt.

[5] The effective interest rate is the spread over LIBOR as of the most recent balance sheet date.