Income Taxes - Significant Components of Company's Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Accrued compensation	$ 184	$ 329
Accrued liabilities	149	121
Tax loss carryforwards	37,986	32,395
Intangible assets	286	307
Share-based compensation	814	728
Tax credits	6,917	5,662
Facility financing lease obligation	1,847	1,861
Deferred revenue	588	0
Other	10	13
Total deferred tax assets	48,781	41,416
Less valuation allowance	(46,604)	(39,174)
Net deferred tax asset	2,177	2,242
Deferred tax liabilities:
Fixed assets	(2,032)	(2,067)
Other	(145)	(175)
Net noncurrent deferred tax asset (liability)	$ 0	$ 0