Difference Between Provision for Income Taxes and Amounts Computed by Applying Federal Statutory Income Tax Rate to Loss before Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory tax	$ (14,906)	$ (12,040)	$ (19,277)
Tax Act revaluation of deferred taxes			81,923
Tax Act deemed income inclusion			1,083
Federal research credits	(1,857)	(1,390)	(1,000)
State research credits	821	655	628
Expiration of federal carryovers	5,472	4,154
Expiration of state carryovers		1,344	1,475
Change in valuation allowance	13,059	9,913	(59,462)
Compensation related items	158	(361)	1,382
State taxes	(1,111)	(1,141)	(803)
Other	269	405	(806)
Provision for income taxes	$ 263	$ 229	$ 3,887