Fair Value Measurements - Estimated Fair Value of Senior Notes (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2012
5.375% Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2014
Senior Notes, interest rate	5.375%
5.375% Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2015
Senior Notes, interest rate	5.375%
5.625% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2020
Senior Notes, interest rate	5.625%

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration