Significant Component of Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Assets [Line Items]
Net operating loss carryforwards	$ 42,715	$ 18,283
Start-up and organizational costs	44,262	40,047
Research and development credit carryforwards	18,388	8,885
Stock compensation	991	702
Capitalized acquisition costs	13,270	6,400
Deferred revenue	1,388
Depreciation	331	170
Other	998	306
Deferred Tax Assets Gross	122,343	74,793
Less valuation allowance	(122,343)	(74,793)
Net deferred tax assets