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Stock-Based Compensation - Additional Information (Detail)
12 Months Ended
Jan. 01, 2018
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
Milestone
$ / shares
shares
Dec. 31, 2015
USD ($)
Milestone
$ / shares
shares
Jul. 02, 2014
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense | $   $ 35,534,000 $ 23,020,000 $ 15,240,000  
Share based compensation granted under plan vest period   4 years      
Total number of options outstanding   7,866,789      
Share based compensation, vest period   1 year      
Share based compensation, term of plan   10 years      
Weighted average grant date fair value per share | $ / shares   $ 41.94 $ 24.97 $ 34.08  
Share option, forfeiture rates   13.30% 9.60% 10.00%  
Non-employees [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share based compensation, term of plan   10 years      
2011 Stock Option Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted   0      
2014 Stock Option Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Common stock available for issuance under stock option plan   2,251,096      
Milestones achieved | Milestone     1 1  
2014 Stock Option Plan [Member] | Milestone One [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of performance based grants that were achieved       35.00%  
2014 Stock Option Plan [Member] | Milestone Two [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of performance based grants that were achieved     50.00% 30.00%  
2014 Stock Option Plan [Member] | Maximum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of increase on outstanding shares of Common stock   4.00%      
2014 Stock Option Plan [Member] | Subsequent Event [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Common stock shares annual increase added to plan 1,680,117        
2014 Employee Stock Purchase Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock initially authorized for issuance under this plan         282,000
Number of shares issued under the plan   30,069      
Accrued expenses | $   $ 300,000      
Restricted Stock Units Vest One Year Anniversary [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units cliff vesting percentage   25.00%      
Restricted Stock Units [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units granted   32,500      
Stock-based compensation expense | $   $ 617,000      
Share based compensation granted under plan vest period   2 years      
Restricted Stock Units [Member] | Restricted Stock Units Vest One Year Anniversary [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units cliff vesting percentage   50.00%      
Restricted stock units vesting period month and year   2018-02      
Restricted Stock Units [Member] | Restricted Stock Units Vest Two Year Anniversary [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units cliff vesting percentage   50.00%      
Restricted stock units vesting period month and year   2019-02      
Performance Shares [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted   449,208 74,039 497,100  
Total unrecognized stock-based compensation expense | $   $ 16,400,000      
Number of shares outstanding and unvested stock options   670,637      
Performance Milestone [Member] | 2014 Stock Option Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense | $     $ 5,000,000 $ 4,800,000  
Performance-Based Stock Options [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense | $   $ 0      
Stock Options [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense | $   $ 34,525,000 $ 22,820,000 14,796,000  
Options granted   2,360,933      
Total number of options outstanding   5,586,593 4,231,807    
Total unrecognized stock-based compensation expense | $   $ 94,400,000      
Weighted average period of unrecognized compensation costs   2 years 6 months 29 days      
Total fair value of options vested | $   $ 24,200,000 $ 24,100,000 9,200,000  
Intrinsic value of options exercised | $   $ 77,700,000 $ 4,600,000 $ 28,400,000