Stock-Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2015	Jul. 23, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option grant, description			Options granted may be either incentive stock options or nonstatutory stock options.
Common stock reserved for issuance	10,822,328		10,822,328	9,833,252
Grant date fair value of options vested, per share			$ 2.72	$ 3.13	$ 0.42
Grant date fair value of options vested			$ 2,400,000	$ 782,000	$ 339,000
Aggregate intrinsic value of option exercised			2,300,000
Unrecognized compensation cost	$ 5,400,000		$ 5,400,000
Weighted average period for recognition of compensation costs			2 years 10 months 24 days
RSUs Granted			151,240
Stock based compensation expenses			$ 2,907,000	1,066,000	318,000
Stock-based compensation expense capitalized			0	0	0
General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based compensation expenses			$ 2,194,000	$ 754,000	$ 218,000
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	151,240		151,240
Weighted average grant date fair value of RSUs granted			$ 3.52
Restricted Stock Units (RSUs) | General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based compensation expenses			$ 532,000
Restricted Stock Units (RSUs) | Board of Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted		112,578
Restricted Stock Units (RSUs) | Executive Officers
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted	18,017
Restricted Stock Units (RSUs) | Consultant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Granted	20,645
Two Thousand Eight Stock Option Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period of stock option plan			10 years
Exercisable period of stock option plan			4 years
Two Thousand Eight Stock Option Plan | Nonstatutory Options | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of fair value of common stock, percentage			85.00%
Two Thousand Eight Stock Option Plan | Ten Percent Stockholder
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period of stock option plan			5 years
Two Thousand Eight and Two Thousand Fifteen Stock Option Plan | Ten Percent Stockholder | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of fair value of common stock, percentage			110.00%
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance						667,670	285,621
Shares issued under ESPP			0	0