Description of Business - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2013 Person	Dec. 31, 2012	Sep. 30, 2013 2.625% convertible senior notes due 2017 [Member]	Sep. 30, 2012 2.625% convertible senior notes due 2017 [Member]
Debt Instrument [Line Items]
Number of patients in research and development activity	1,700
Cumulative net losses	$ (336,929)	$ (291,548)
Debt instrument, interest rate			2.625%	2.625%

The cumulative amount of the reporting entity's undistributed earnings or deficit.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.31(a)(3))

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

Name:	us-gaap_RetainedEarningsAccumulatedDeficit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant