Significant Component of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Net operating loss carryforwards	$ 124,115	$ 106,430
Deferred tax assets:
Start-up and organizational costs	30,480	33,977
Research and development credit carryforwards	35,130	33,684
Stock compensation	1,087	990
Capitalized acquisition costs	4,501	5,160
Lease liability	626
Depreciation	176	132
Other	1,186	920
Deferred Tax Assets Gross	197,301	181,293
Less valuation allowance	(196,696)	(181,293)
Total deferred tax assets	605	0
Deferred tax liabilities:
Right of use asset	(605)	0
Total deferred tax liabilities	(605)	0
Net deferred taxes	$ 0	$ 0