Description of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	May 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Place of incorporation			Arizona
Year of incorporation			2002
Place of reincorporation			Delaware
Date of reincorporation			2015-03
Common stock, authorized					150,000,000	400,000,000
Reverse split of issued and outstanding common stock			1:20
Accumulated deficit	$ (182,170)		$ (182,170)	$ (167,257)
Cash and cash equivalents	9,667		9,667	9,125	$ 13,438		$ 2,013
Short-term investments	18,931		18,931	$ 3,898
Proceeds from issuance of private placement	$ 14,000	$ 10,000	$ 10,000