Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2013

Fair Value Measurements Tables [Abstract]

Fair Value By Balance Sheet Grouping [Text Block]

Assets:		Level 1		Level 2		Level 3		Total
Current derivative asset	$	-	$	4,027	$	-	$	4,027
Liabilities:
Current derivative liability	$	-	$	6,887	$	-	$	6,887

Schedule of Fair Value of Financial Instruments

		June 30, 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	$	106,322	$	100,000	$	107,801
7.31% Notes due 2016, issued 2009		62,000		70,333		62,000		72,046
4.98% Notes due 2017, issued 2010		116,000		124,254		116,000		127,109
5.92% Notes due 2018, issued 2008		200,000		221,832		200,000		230,062
7.77% Notes due 2019, issued 2009		173,000		208,642		173,000		219,045
5.50% Notes due 2020, issued 2010		207,000		222,695		207,000		234,552
4.51% Notes due 2020, issued 2010		315,000		312,738		315,000		331,329
5.60% Notes due 2022, issued 2010		87,000		92,293		87,000		98,526
4.66% Notes due 2022, issued 2010		35,000		33,891		35,000		36,361
5.85% Notes due 2025, issued 2010		90,000		95,017		90,000		102,096
4.91% Notes due 2025, issued 2010		175,000		167,345		175,000		179,677
Credit Facility		320,000		320,000		277,000		277,000
	$	1,880,000	$	1,975,362	$	1,837,000	$	2,015,604