Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.20.1
Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Feb. 28, 2020
Jan. 03, 2020
Jul. 18, 2019
Feb. 25, 2019
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2017
Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Authorized capital stock         520,000,000      
Common stock, par value         $ 0.0001     $ 0.0001
Common stock, shares authorized         500,000,000     500,000,000
Preferred stock, par value         $ 0.0001      
Preferred stock, shares authorized         20,000,000      
Preferred stock, shares outstanding         0     0
Proceeds from sale of common stock, net         $ 24,277,000 $ 0    
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         16,745,854      
2014 Equity Incentive Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Shares of common stock, reserved for issuance         14,316,451      
Aggregate number of awards available for grant to be issued         2,483,425      
Outstanding options and RSUs         11,833,026      
Inducement Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Shares of common stock, reserved for issuance         1,196,086      
Aggregate number of awards available for grant to be issued         272,336      
Outstanding options and RSUs         923,750      
Restricted Stock Units (RSUs)                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Unrecognized stock-based compensation expense         $ 63,900,000      
Unrecognized stock-based compensation weighted average recognition period         2 years 10 months 24 days      
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         3 years      
Stock options, issued             275,000  
Unrecognized stock-based compensation         $ 71,100,000      
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]                
Warrants outstanding         2,888,526,000      
Underwritten Public Offering | Warrant                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
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         1,528,216      
Common stock average price         $ 15.50      
Proceeds from sale of common stock, gross         $ 23,700,000      
Proceeds from sale of common stock, net   $ 1,200,000     23,100,000      
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%        
2019 ATM Facility | Cowen                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Common stock value remaining to be sold         25,900,000      
2020 ATM Facility | Cowen                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Common stock value remaining to be sold         $ 100,000,000.0