Property and Equipment, Net - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 721,000	$ 654,000
Cambridge Massachusetts \| Lease Agreements
Property, Plant and Equipment [Line Items]
Construction in progress and facility lease obligation	$ 19,500,000
Year in which leased facility will be available for occupancy	2015

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Name:	us-gaap_DepreciationDepletionAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration