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Stock Option Plans - Narrative (Details)
3 Months Ended
Mar. 31, 2018
compensation_plan
shares
Mar. 29, 2018
$ / shares
Dec. 31, 2017
shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Number of stock option plans | compensation_plan 2    
Option expiration period 10 years    
Option vesting period 4 years    
Closing share price (in usd per share) | $ / shares   $ 50.97  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 905,670   913,320
Weighted average remaining contractual life of the Company's outstanding options 7 years 3 months 9 days    
Weighted average remaining contractual life of the Company's exercisable options 6 years 3 months 4 days    
2015      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 189,375    
2016      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 213,375    
2017      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 232,500