Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2016

Fair Value Measurements Tables [Abstract]

Schedule of Fair Value of Financial Instruments

		September 30, 2016(1)				December 31, 2015
		Carrying		Estimated		Carrying		Estimated
		Amount		Fair Value		Amount		Fair Value
7.31% Notes due March 2016, issued 2009		62,000		64,266		62,000		63,604
4.98% Notes due January 2017, issued 2010		116,000		122,371		116,000		113,420
5.92% Notes due March 2018, issued 2008		200,000		212,433		200,000		191,985
5.75% Notes due December 2018, issued 2013		450,000		389,123		450,000		111,451
7.77% Notes due March 2019, issued 2009		173,000		191,099		173,000		174,488
5.50% Notes due January 2020, issued 2010		207,000		219,783		207,000		185,052
4.51% Notes due October 2020, issued 2010		315,000		322,069		315,000		258,520
5.60% Notes due January 2022, issued 2010		87,000		92,099		87,000		73,034
4.66% Notes due October 2022, issued 2010		35,000		36,228		35,000		25,558
6.125% Notes due October 2024, issued 2014		850,000		741,912		850,000		206,321
5.85% Notes due January 2025, issued 2010		90,000		95,232		90,000		70,756
4.91% Notes due October 2025, issued 2010		175,000		183,614		175,000		115,911
Credit Facility due October 2016		999,000		999,000		630,000		630,000
	$	3,759,000	$	3,669,229	$	3,390,000	$	2,220,100