Stock-Based Compensation - Summary of Stock Option Activity (Detail)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding beginning balance, Shares Subject to Stock Options | shares	883,837
Granted, Shares Subject to Stock Options | shares	809,534
Cancelled, Shares Subject to Stock Options | shares	(98,477)
Options outstanding ending balance, Shares Subject to Stock Options | shares	1,594,894
Options exercisable, Shares Subject to Stock Options | shares	594,069
Options outstanding beginning balance, Weighted-Average Exercise Price | $ / shares	$ 4.28
Granted, Weighted-Average Exercise Price | $ / shares	1.23
Cancelled, Weighted-Average Exercise Price | $ / shares	5.29
Options outstanding ending balance, Weighted-Average Exercise Price | $ / shares	2.67
Options exercisable, Weighted-Average Exercise Price | $ / shares	$ 4.14
Options outstanding, Weighted-Average Remaining Contractual Term	9 years 22 days
Options exercisable, Weighted-Average Remaining Contractual Term	8 years 7 months 28 days