Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2014

Fair Value Measurements Tables [Abstract]

Fair Value By Balance Sheet Grouping [Text Block]

		Level 1		Level 2		Level 3		Total
Liabilities:
Current derivative liability	$	-	$	40,007	$	-	$	40,007

Schedule of Fair Value of Financial Instruments

		June 30, 2014				December 31, 2013
		Carrying		Estimated		Carrying		Estimated
		Amount		Fair Value		Amount		Fair Value
5.45% Notes due March 2015, issued 2008	$	100,000	$	103,950	$	100,000	$	105,913
7.31% Notes due March 2016, issued 2009		62,000		68,371		62,000		70,228
4.98% Notes due January 2017, issued 2010		116,000		123,818		116,000		126,342
5.92% Notes due March 2018, issued 2008		200,000		222,247		200,000		226,127
5.75% Notes due December 2018, issued 2013		450,000		463,634		450,000		466,946
7.77% Notes due March 2019, issued 2009		173,000		208,034		173,000		211,877
5.50% Notes due January 2020, issued 2010		207,000		226,818		207,000		229,068
4.51% Notes due October 2020, issued 2010		315,000		323,556		315,000		323,732
5.60% Notes due January 2022, issued 2010		87,000		95,464		87,000		95,736
4.66% Notes due October 2022, issued 2010		35,000		35,703		35,000		35,494
5.85% Notes due January 2025, issued 2010		90,000		99,815		90,000		99,142
4.91% Notes due October 2025, issued 2010		175,000		178,089		175,000		175,744
Credit Facility due October 2016		427,000		427,000		460,000		460,000
	$	2,437,000	$	2,576,499	$	2,470,000	$	2,626,349