Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2014

Fair Value Measurements Tables [Abstract]

Fair Value By Balance Sheet Grouping [Text Block]

Assets:		Level 1		Level 2		Level 3		Total
Current derivative asset	$	-	$	290	$	-	$	290
Liabilities:
Current derivative liability	$	-	$	62,486	$	-	$	62,486

Schedule of Fair Value of Financial Instruments

		March 31, 2014				December 31, 2013
		Carrying		Estimated		Carrying		Estimated
		Amount		Fair Value		Amount		Fair Value
5.45% Notes due March 2015, issued 2008	$	100,000	$	103,491	$	100,000	$	105,913
7.31% Notes due March 2016, issued 2009		62,000		68,071		62,000		70,228
4.98% Notes due January 2017, issued 2010		116,000		123,107		116,000		126,342
5.92% Notes due March 2018, issued 2008		200,000		220,516		200,000		226,127
5.75% Notes due December 2018, issued 2013		450,000		471,614		450,000		466,946
7.77% Notes due March 2019, issued 2009		173,000		205,850		173,000		211,877
5.50% Notes due January 2020, issued 2010		207,000		224,213		207,000		229,068
4.51% Notes due October 2020, issued 2010		315,000		319,195		315,000		323,732
5.60% Notes due January 2022, issued 2010		87,000		94,138		87,000		95,736
4.66% Notes due October 2022, issued 2010		35,000		35,167		35,000		35,494
5.85% Notes due January 2025, issued 2010		90,000		98,209		90,000		99,142
4.91% Notes due October 2025, issued 2010		175,000		175,095		175,000		175,744
Credit Facility due October 2016		415,000		415,000		460,000		460,000
	$	2,425,000	$	2,553,666	$	2,470,000	$	2,626,349