Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Apr. 27, 2011 Class A common stock [Member]	Mar. 31, 2013 Common stock equivalents 1.875% Notes [Member]	Mar. 31, 2013 Common stock equivalents 4.0% Notes [Member]
Class of Stock [Line Items]
Interest rate for senior notes			1.875%	4.00%
Stock repurchase authorized	$ 150.0	$ 300.0
New stock repurchase authorized program	$ 300.0

Interest rate stated in the contractual debt agreement.

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)(1))

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

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