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Stock-Based Compensation Expense - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Mar. 15, 2019
Sep. 14, 2018
Mar. 15, 2018
Jun. 30, 2019
Jun. 30, 2018
Sep. 17, 2018
Mar. 16, 2018
Sep. 18, 2017
Mar. 16, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Vesting period       4 years          
Purchase price of common stock by employees (as a percent)       85.00%          
Issuance of common stock under Employee Stock Purchase Plan       $ 2,634 $ 1,632        
Employee Stock Purchase Plan [Member] | Maximum [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Employee withholding percentage       15.00%          
Restricted Stock And Restricted Stock Units [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unrecognized compensation expense       $ 97,100          
Unrecognized compensation expense, recognition period       2 years 9 months 18 days          
Options to Purchase Common Stock [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unrecognized compensation expense, recognition period       1 year 6 months          
Unrecognized compensation cost, stock options       $ 4,500          
Stock options vested, fair value       $ 3,800          
Employee Stock [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Common stock issued to employees (in shares) 110,822 96,108 123,607            
Issuance of common stock under Employee Stock Purchase Plan $ 2,600 $ 2,000 $ 1,600            
Share issued, price per share (in dollars per share)           $ 30.46 $ 21.96 $ 14.78 $ 12.96
Closing price of shares issued (in dollars per share)           $ 35.84 $ 25.84 $ 17.39 $ 15.25