Stockholders' Equity - Summary of Stock Option Transactions (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Shares Available for Grant
Options Available, Amendment to plan to authorize additional shares	8,929,188
Stock Options [Member]
Shares Available for Grant
Options Available, Beginning balance	958,856
Options Available, Additional shares authorized	671,478
Options Available, Granted	(3,113,777)
Options Available, Exercised	0
Options Available, Canceled/Forfeited	108,191
Options Available, Ending balance	7,553,936	958,856
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance	2,908,430
Options granted	3,113,777
Options canceled/forfeited	(108,191)
Ending balance	5,914,016	2,908,430
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 3.42
Options granted (in dollars per share)	0.61
Options canceled/forfeited (in dollars per share)	3.49
Ending balance (in dollars per share)	$ 1.94	$ 3.42
Weighted Average Remaining Contractual Term
Options outstanding at end of period	8 years 11 months 23 days	8 years 5 months 23 days
Options vested at end of period	8 years 4 months 13 days
Options vested and expected to vest at end of period	8 years 11 months 23 days
Options vested at end of period (shares)	2,503,001
Options vested at end of period (in dollars per share)	$ 2.91
Options vested and expected to vest at end of period (shares)	5,914,016
Options vested and expected to vest at end of period (in dollars per share)	$ 1.94