Significant Component of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets [Line Items]
Net operating loss carryforwards	$ 100,790	$ 96,215
Start-up and organizational costs	59,360	64,942
Research and development credit carryforwards	34,845	29,564
Stock compensation	2,014	1,997
Capitalized acquisition costs	9,389	10,429
Deferred revenue	18,636	2,695
Depreciation	227	251
Other	1,537	1,673
Deferred Tax Assets Gross	226,798	207,766
Less valuation allowance	(226,798)	(207,766)
Effective tax rate	$ 0	$ 0