Description of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Description Of Business And Basis Of Presentation [Line Items]
Place of incorporation		Arizona
Year of incorporation		2002
Place of reincorporation		Delaware
Date of reincorporation		2015-03
Accumulated deficit		$ (164,297)	$ (151,550)
Cash and cash equivalents		2,930	2,013	$ 10,473	$ 23,973
Short-term investments		$ 12,767	$ 48,547
Senior Secured Term Loan Facility [Member]
Description Of Business And Basis Of Presentation [Line Items]
Repayment of term loan	$ 25,000
Interest paid, prepayment and end-of-term payments	$ 1,300