Significant Component of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets [Line Items]
Net operating loss carryforwards	$ 96,215	$ 79,050
Start-up and organizational costs	64,942	38,562
Research and development credit carryforwards	29,564	26,112
Stock compensation	1,997	1,181
Capitalized acquisition costs	10,429	11,376
Deferred revenue	2,695	534
Depreciation	251	208
Other	1,673	1,547
Deferred Tax Assets Gross	207,766	158,570
Less valuation allowance	(207,766)	(158,570)
Effective tax rate	$ 0	$ 0