Description of Business - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Place of incorporation	Arizona
Year of incorporation	2002
Place of reincorporation	Delaware
Date of reincorporation	2015-03
Reverse split of issued and outstanding common stock	1:20
Stock split conversion ratio	0.05
Common stock, authorized | shares	150,000,000	150,000,000
Accumulated deficit	$ 178,366	$ 167,257
Cash and cash equivalents	11,998	9,125	$ 2,013
Short-term investments	9,825	3,898
Net losses	(13,480)	(15,707)
Net cash used in operations	$ (13,631)	$ (13,965)