Investments with Continuous Unrealized Losses and Related Fair Value (Detail) (Commercial Paper, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Investments With Continuous Unrealized Losses For Less Than 12 Months, Fair Value	$ 19,995
Investments With Continuous Unrealized Losses For Less Than 12 Months, Unrealized Losses	$ (4)

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant