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 6 Months Ended
Mar. 31, 2018
Jan. 31, 2018
Mar. 31, 2017
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Proceeds from sale of common stock, net           $ 47,586,000 $ 9,326,000
Shares of common stock ,reserved for issuance       13,303,966   13,303,966  
Common stock, shares exercised           622,982 0
Option intrinsic value, exercised           $ 11,300,000  
Net tax benefits related to exercised options           0  
Estimated fair value of stock option, vested           8,200,000 $ 7,400,000
Stock-based compensation expense       $ 7,998,000 $ 5,656,000 $ 15,013,000 $ 11,003,000
Restricted Stock Units              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Weighted average grant date fair value per share           $ 36.69 $ 15.78
Unrecognized stock-based compensation expense       37,500,000   $ 37,500,000  
Unrecognized stock-based compensation weighted average recognition period           2 years 9 months 18 days  
Aggregate intrinsic value       66,200,000   $ 66,200,000  
Restricted stock units, settled           380,034 253,399
Restricted stock units, issued net of tax withholdings           233,836 49,691
Restricted stock units withheld for tax obligations           87,954 21,201
Restricted stock units withheld for tax obligations, value           $ 3,400,000 $ 300,000
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  
Stock options, issued           275,000  
Unrecognized stock-based compensation       $ 52,800,000   $ 52,800,000  
2014 Equity Incentive Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Shares of common stock ,reserved for issuance       10,851,962   10,851,962  
Aggregate number of awards available for grant to be issued       3,958,128   3,958,128  
Outstanding options and RSUs       6,893,834   6,893,834  
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       882,500   882,500  
Outstanding options and RSUs       367,500   367,500  
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           $ 200,000 $ 100,000
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          
Common stock, shares sold 4,928,571 7,675,072          
At The Market Offering | Cowen              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Common stock, shares issued       1,007,806   1,007,806  
Common stock, shares sold       1,007,806   1,007,806  
Common stock average price       $ 48.52   $ 48.52  
Proceeds from sale of common stock, gross       $ 48,900,000   $ 48,900,000  
Proceeds from sale of common stock, net       47,600,000   47,600,000  
Common stock value remained available to be sold       $ 6,100,000   $ 6,100,000  
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%