Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.19.1
Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Feb. 25, 2019
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2017
Dec. 31, 2018
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
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 to employees and non-employees generally vest over four years and expire in seven to ten years.      
Ownership percent   10.00%      
Shares of common stock, reserved for issuance   14,752,922      
Common stock, shares exercised   159,355 309,497    
Option intrinsic value, exercised   $ 3,100,000 $ 4,900,000    
Net tax benefits related to exercised options   0      
Estimated fair value of stock option, vested   12,000,000 3,300,000    
Stock purchase, value   2,898,000 6,196,000    
Stock-based compensation expense   $ 12,269,000 7,014,000    
2014 Equity Incentive Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares of common stock, reserved for issuance   12,251,242      
Aggregate number of awards available for grant to be issued   4,188,091      
Outstanding options and RSUs   8,063,151      
Inducement Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares of common stock, reserved for issuance   1,250,000      
Aggregate number of awards available for grant to be issued   720,000      
Outstanding options and RSUs   530,000      
2014 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Percentage of employees purchase price of common stock   85.00%      
Shares of common stock, reserved for issuance   1,142,014      
Aggregate number of awards available for grant to be issued   1,142,014      
Unrecognized stock-based compensation expense   $ 200,000      
Employee stock purchase plan description   (i) the beginning of a 12-month offering period, or (ii) at the end of one of the two related 6-month purchase periods      
Stock-based compensation expense   $ 200,000 $ 100,000    
Shares purchased   0 0    
Restricted Stock Units          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Weighted average grant date fair value per share   $ 38.42 $ 35.80    
Unrecognized stock-based compensation expense   $ 55,200,000      
Unrecognized stock-based compensation weighted average recognition period   2 years 10 months 24 days      
Aggregate intrinsic value   $ 73,900,000      
Restricted stock units, settled   316,473 336,240    
RSU settlements, net of shares withheld, shares   289,348 229,854    
Restricted stock units withheld for tax obligations   118,747 86,359    
Restricted stock units withheld for tax obligations, value   $ 4,600,000 $ 3,400,000    
Restricted Stock Units | Following Service Termination Date          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share based compensation award expiration period   2 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   $ 83,700,000      
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 | Restricted Stock Units | From Date Of Grant          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share based compensation award expiration period   7 years      
Minimum | Employees And Non Employees          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share based compensation award expiration period   7 years      
Maximum | 2014 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock purchase, value   $ 25,000      
Annual increase in EIP/ESPP, subject to other limitations   1.00%      
Maximum increase in number of shares available for issuance   230,769      
Maximum | Restricted Stock Units | From Date Of Grant          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share based compensation award expiration period   10 years      
Maximum | Employees And Non Employees          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share based compensation award expiration period   10 years      
At The Market Offering | Cowen          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock, shares issued   0      
Common stock value remaining to be sold   $ 100,000,000      
At The Market Offering | Cowen | Maximum          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock aggregate offering price $ 100,000,000        
Percentage of commission to be paid on gross sales proceeds of common stock sold 3.00%