Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	$ 251,628	$ 197,959
Cash, including restricted cash	32,105	37,614
Total cash and investments in marketable securities	309,071	262,026
Corporate Notes and Bonds [Member] \| Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	171,194	138,515
Corporate Commercial Paper [Member] \| Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	80,434	59,444
Money Market Funds [Member] \| Fair Value Hierarchy Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Money market funds	$ 25,338	$ 26,453

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

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