Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Mar. 31, 2018
Jan. 31, 2018
Mar. 31, 2017
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Proceeds from sale of common stock, net           $ 47,586,000 $ 19,206,000
Shares of common stock, reserved for issuance       12,992,937   12,992,937  
Common stock, shares exercised           781,191 0
Option intrinsic value, exercised           $ 13,900,000  
Net tax benefits related to exercised options           0  
Estimated fair value of stock option, vested           12,700,000 $ 10,900,000
Stock-based compensation expense       $ 9,252,000 $ 6,000,000 $ 24,264,000 $ 17,003,000
Restricted Stock Units              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Weighted average grant date fair value per share           $ 34.61 $ 15.07
Unrecognized stock-based compensation expense       33,000,000   $ 33,000,000  
Unrecognized stock-based compensation weighted average recognition period           2 years 8 months 12 days  
Aggregate intrinsic value       59,300,000   $ 59,300,000  
Restricted stock units, settled           634,851 290,534
Restricted stock units, issued net of tax withholdings           439,986 51,592
Restricted stock units withheld for tax obligations           189,951 21,895
Restricted stock units withheld for tax obligations, value           $ 7,500,000 $ 400,000
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 1 month 6 days  
Stock options, issued           275,000  
Unrecognized stock-based compensation       $ 67,900,000   $ 67,900,000  
2014 Equity Incentive Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Shares of common stock, reserved for issuance       10,540,933   10,540,933  
Aggregate number of awards available for grant to be issued       3,457,163   3,457,163  
Outstanding options and RSUs       7,083,770   7,083,770  
2018 Inducement Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Shares of common stock, reserved for issuance       1,250,000   1,250,000  
Aggregate number of awards available for grant to be issued       720,000   720,000  
Outstanding options and RSUs       530,000   530,000  
2014 Employee Stock Purchase Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Shares of common stock, reserved for issuance       943,338   943,338  
Aggregate number of awards available for grant to be issued       943,338   943,338  
Stock-based compensation expense           $ 500,000 $ 400,000
Shares purchased           77,100 43,962
Options Granted Outside the Equity Plans              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Shares of common stock, reserved for issuance       258,666   258,666  
Underwritten Public Offering              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Common stock, shares issued 4,928,571 7,675,072          
Shares issued, price per share $ 35.00 $ 18.25          
Net proceeds from sale of common stock $ 161,900,000 $ 131,400,000          
At The Market Offering | Cowen              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Common stock, shares issued           1,007,806  
Common stock average price           $ 48.52  
Proceeds from sale of common stock, gross           $ 48,900,000  
Proceeds from sale of common stock, net           47,600,000  
Common stock value remained available to be sold       $ 6,100,000   $ 6,100,000  
Shares sold under ATM Facility       0      
At The Market Offering | Cowen | Maximum              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Common stock aggregate offering price     $ 75,000,000        
Percentage of commission to be paid on gross sales proceeds of common stock sold     3.00%