Component of Accrued Expenses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accrued Liabilities [Line Items]
Professional services	$ 835	$ 1,131
Clinical consulting services	9,628	6,913
Preclinical services	411	1,093
Manufacturing services	3,217	767
Accrued vacation	452	307
Other consulting services	903	347
Payroll taxes and benefits	585	263
Severance	474
Employee compensation	11
Accrued expenses	$ 16,516	$ 10,821