Carrying Amount of the Company's Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule Of Carrying Amount Of Senior Notes [Line Items]
Senior Notes	$ 744,470	$ 744,108
5.375% Senior Notes Due 2014 [Member]
Schedule Of Carrying Amount Of Senior Notes [Line Items]
Senior Notes	249,528	249,438
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2014
5.375% Senior Notes Due 2015 [Member]
Schedule Of Carrying Amount Of Senior Notes [Line Items]
Senior Notes	249,876	249,857
Senior Notes, interest rate	5.375%
Senior Notes, maturity date	2015
5.625% Senior Notes Due 2020 [Member]
Schedule Of Carrying Amount Of Senior Notes [Line Items]
Senior Notes	$ 245,066	$ 244,813
Senior Notes, interest rate	5.625%
Senior Notes, maturity date	2020