Business - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Nature Of Business [Line Items]
Accumulated deficit	$ 315,215	$ 283,724

Cumulative net losses reported during the development stage.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 915

-SubTopic 210

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6472335&loc=d3e37729-110921

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