Fair Value Measurements (Estimated Fair Value Of Senior Notes) (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	9 Months Ended
	Jul. 07, 2011	Sep. 30, 2011	Dec. 31, 2010
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		$ 1,006,656	$ 1,242,815
7% Senior Notes Due 2012 [Member] | Fair Value, Inputs, Level 2 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		86,110	149,650
Estimated Fair Value		92,347	160,493
5 1/2% Senior Notes Due 2013 [Member] | Fair Value, Inputs, Level 2 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		176,615	349,748
Estimated Fair Value		189,782	362,198
Fair Value, Inputs, Level 2 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		1,006,656	1,242,815
Estimated Fair Value		1,030,479	1,274,224
Fair Value, Inputs, Level 2 [Member] | 5 3/8% Medium-Term Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		249,394	249,266
Estimated Fair Value		265,000	255,683
Fair Value, Inputs, Level 2 [Member] | 5 3/8% Medium-Term Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		249,848	249,821
Estimated Fair Value		261,675	251,450
Fair Value, Inputs, Level 2 [Member] | 5 5/8% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		244,689	244,330
Estimated Fair Value		221,675	244,400
7% Senior Notes Due 2012 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		86,110	149,650
Interest rate	7.00%	7.00%
Maturity date	2012	2012
5 1/2% Senior Notes Due 2013 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		176,615	349,748
Interest rate	5.50%	5.50%
Maturity date	2013	2013
5 3/8% Medium-Term Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		249,394	249,266
Interest rate		5.375%
Maturity date		2014
5 3/8% Medium-Term Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		249,848	249,821
Interest rate		5.375%
Maturity date		2015
5 5/8% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Recorded Amount		$ 244,689	$ 244,330
Interest rate		5.375%
Maturity date		2020
5 5/8% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Interest rate		5.625%
Maturity date		2020