Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.20.2
Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Oct. 02, 2020
Feb. 28, 2020
Jan. 03, 2020
Jul. 18, 2019
Feb. 25, 2019
Sep. 30, 2020
Jun. 30, 2020
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2017
Dec. 31, 2019
Jul. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Authorized capital stock           520,000,000   520,000,000        
Common stock, par value           $ 0.0001   $ 0.0001     $ 0.0001  
Common stock, shares authorized           500,000,000   500,000,000     500,000,000  
Preferred stock, par value           $ 0.0001   $ 0.0001        
Preferred stock, shares authorized           20,000,000   20,000,000        
Preferred stock, shares outstanding           0   0     0  
Proceeds from sale of common stock, net               $ 58,045,000 $ 12,630,000      
Stock option granted description terms               the exercise price of an option granted to a 10% shareholder cannot be less than 110% of the estimated fair value of the shares on the date of grant. Options granted generally vest over four years and expire in seven to ten years.        
Ownership percent               10.00%        
Shares of common stock, reserved for issuance           17,505,050   17,505,050        
2014 Equity Incentive Plan                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Shares of common stock, reserved for issuance           13,803,560   13,803,560        
Aggregate number of awards available for grant to be issued           2,434,930   2,434,930        
Outstanding options and RSUs           11,368,630   11,368,630        
Inducement Plan                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Shares of common stock, reserved for issuance           2,634,836   2,634,836        
Aggregate number of awards available for grant to be issued           1,734,211   1,734,211        
Outstanding options and RSUs           900,625   900,625        
Additional shares of common stock, reserved for issuance           1,500,000   1,500,000        
Restricted Stock Units (RSUs)                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Unrecognized stock-based compensation expense           $ 45,500,000   $ 45,500,000        
Unrecognized stock-based compensation weighted average recognition period               2 years 6 months        
Restricted Stock Units (RSUs) | From Date Of Grant                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Share based compensation, vesting period               4 years        
Employees And Non Employees                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Share based compensation, vesting period               4 years        
Vested and Unvested Options                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Unrecognized stock-based compensation weighted average recognition period               2 years 8 months 12 days        
Stock options, issued                   275,000    
Unrecognized stock-based compensation           $ 55,400,000   $ 55,400,000        
Maximum | Employees And Non Employees                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Share based compensation award expiration period               10 years        
Minimum                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Percentage of employees purchase price of common stock               100.00%        
Minimum | 10% Shareholder                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Percentage of employees purchase price of common stock               110.00%        
Minimum | Employees And Non Employees                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Share based compensation award expiration period               7 years        
Underwritten Public Offering                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Common stock, shares issued             12,633,039          
Shares issued, price per share             $ 11.32          
Option price to purchase shares             $ 11.32          
Proceeds from sale of common stock, gross             $ 201,800,000          
Net proceeds from sale of common stock             $ 189,300,000          
Common stock, shares issued             12,633,039          
Proceeds from sale of common stock, gross             $ 201,800,000          
Underwritten Public Offering | 2020 Warrants                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Warrants outstanding           2,866,961   2,866,961        
Underwritten Public Offering | 2019 Warrants                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Number of warrants issued                       2,945,026
Warrants outstanding           2,888,526   2,888,526        
Underwritten Public Offering | Maximum                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Additional shares of our common stock             2,325,000          
Underwritten Public Offering | Warrant                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Number of warrants issued             2,866,961          
Warrant, price per share             $ 11.3199          
Number of securities called by each warrant       1                
Warrants, exercise price       $ 0.0001                
Warrants, term       7 years                
Maximum ownership Percentage       9.99%                
Underwritten Public Offering | Warrant | Maximum                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Maximum ownership Percentage       19.99%                
Underwritten Public Offering | Warrant | Minimum                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Prior notice period       61 days                
At The Market Offering | Cowen                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Common stock, shares issued           2,581,768   4,109,984        
Proceeds from sale of common stock, gross           $ 35,000,000.0   $ 58,700,000        
Common stock, shares issued           2,581,768   4,109,984        
Common stock average price           $ 13.56   $ 14.28        
Proceeds from sale of common stock, gross           $ 35,000,000.0   $ 58,700,000        
Proceeds from sale of common stock, net     $ 1,200,000     34,100,000   57,100,000        
At The Market Offering | Cowen | Subsequent Event                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Proceeds from sale of common stock, net $ 300,000                      
At The Market Offering | Maximum | Cowen                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Common stock aggregate offering price   $ 100,000,000.0     $ 100,000,000.0              
Percentage of commission to be paid on gross sales proceeds of common stock sold   3.00%     3.00%              
2020 ATM Facility | Cowen                        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                        
Common stock value remaining to be sold           $ 90,900,000   $ 90,900,000