Estimated Fair Value Of Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	$ 744,470	$ 744,108
5.375% Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	249,528	249,438
Senior Notes, interest rate	5.375%
5.375% Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	249,876	249,857
Senior Notes, interest rate	5.375%
5.625% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	245,066	244,813
Senior Notes, interest rate	5.625%
Carrying Amount [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	744,470	744,108
Carrying Amount [Member] | 5.375% Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	249,528	249,438
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2014
Carrying Amount [Member] | 5.375% Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	249,876	249,857
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2015
Carrying Amount [Member] | 5.625% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	245,066	244,813
Senior Notes, interest rate	5.625%
Senior Notes, maturity date	2020
Fair Value [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	779,933	734,217
Fair Value [Member] | 5.375% Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	263,275	254,667
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2014
Fair Value [Member] | 5.375% Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	266,058	252,083
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2015
Fair Value [Member] | 5.625% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes	$ 250,600	$ 227,467
Senior Notes, interest rate	5.625%
Senior Notes, maturity date	2020