Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Measurements Tables [Abstract]

Fair Value of Long-Term Debt

		December 31, 2012				December 31, 2011
		Carrying		Estimated		Carrying		Estimated
		Amount		Fair Value		Amount		Fair Value
Long-Term Debt:
5.45% Notes due 2015, issued 2008	$	100,000	$	107,801	$	100,000	$	111,475
7.31% Notes due 2016, issued 2009		62,000		72,046		62,000		74,817
4.98% Notes due 2017, issued 2010		116,000		127,109		116,000		128,570
5.92% Notes due 2018, issued 2008		200,000		230,062		200,000		231,091
7.77% Notes due 2019, issued 2009		173,000		219,045		173,000		219,552
5.50% Notes due 2020, issued 2010		207,000		234,552		207,000		229,423
4.51% Notes due 2020, issued 2010		315,000		331,329		315,000		318,925
5.60% Notes due 2022, issued 2010		87,000		98,526		87,000		94,165
4.66% Notes due 2022, issued 2010		35,000		36,361		35,000		34,631
5.85% Notes due 2025, issued 2010		90,000		102,096		90,000		99,022
4.91% Notes due 2025, issued 2010		175,000		179,677		175,000		173,835
Credit Facility		277,000		277,000		343,000		343,000
	$	1,837,000	$	2,015,604	$	1,903,000	$	2,058,506