Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Measurements Tables [Abstract]

Fair Value By Balance Sheet Grouping [Text Block]

		Level 1		Level 2		Level 3		Total
Liabilities:
Current derivative liability	$	-	$	44,715	$	-	$	44,715

Schedule of Fair Value of Financial Instruments

		March 31, 2013				December 31, 2012
		Carrying		Estimated		Carrying		Estimated
		Amount		Fair Value		Amount		Fair Value
Long-Term Debt:
5.45% Notes due 2015, issued 2008	$	100,000	$	106,060	$	100,000	$	107,801
7.31% Notes due 2016, issued 2009		62,000		70,494		62,000		72,046
4.98% Notes due 2017, issued 2010		116,000		125,412		116,000		127,109
5.92% Notes due 2018, issued 2008		200,000		225,909		200,000		230,062
7.77% Notes due 2019, issued 2009		173,000		213,944		173,000		219,045
5.50% Notes due 2020, issued 2010		207,000		230,368		207,000		234,552
4.51% Notes due 2020, issued 2010		315,000		325,882		315,000		331,329
5.60% Notes due 2022, issued 2010		87,000		96,325		87,000		98,526
4.66% Notes due 2022, issued 2010		35,000		35,558		35,000		36,361
5.85% Notes due 2025, issued 2010		90,000		100,327		90,000		102,096
4.91% Notes due 2025, issued 2010		175,000		177,595		175,000		179,677
Credit Facility		373,000		373,000		277,000		277,000
	$	1,933,000	$	2,080,874	$	1,837,000	$	2,015,604