Investments - Fair Value of Short-Term Available-for-Sale and Trading Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	$ 306,513	$ 299,715
Fair value of short-term investments	306,513	300,715
Bankers' Acceptance Drafts [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	637	491
Time Deposits [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	3,442	3,439
Commercial Paper and Certificates of Deposit [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	127,524	114,984
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	16,826	18,351
U.S. Agency Obligations [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	158,084	162,450
Mutual Funds [Member]
Schedule of Investments [Line Items]
Fair value of short-term investments, mutual funds		$ 1,000

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

+ References

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- Definition

Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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