Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Oct. 31, 2016 ft² Suite	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Other Commitments [Line Items]
Rent expense		$ 300,000	$ 100,000	$ 42,000
Palo Alto, California [Member]
Other Commitments [Line Items]
Lease Commencement Date		Jan. 04, 2017	Apr. 01, 2015
Long-term operating lease expiry period			36 months
Number of additional suites | Suite	2
Total leased space | ft²	3,877
Long-term operating lease expiry period month and year		2018-03
Lease renewal term		2 years
Sublease commenced date		Jan. 26, 2016
Sublease expiration date		Mar. 30, 2017
Palo Alto, California [Member] | Other Assets [Member]
Other Commitments [Line Items]
Security deposit of collateral for lease			$ 21,000
Security deposit for sublease		$ 16,000
Palo Alto, California [Member] | Other Assets [Member] | Maximum [Member]
Other Commitments [Line Items]
Security deposit of collateral for lease		$ 49,000