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Stock-Based Compensation - Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Options    
Beginning balance (in shares) 983,512  
Granted (in shares) 62,020  
Exercised (in shares) (154,418)  
Canceled (in shares) (12,866)  
Ending balance (in shares) 878,248 983,512
Exercisable at period end (in shares) 711,207  
Weighted Average Exercise Price    
Beginning balance (in dollars per share) $ 40.62  
Granted (in dollars per share) 71.79  
Exercised (in dollars per share) 18.32  
Canceled (in dollars per share) 67.61  
Ending balance (in dollars per share) 46.34 $ 40.62
Exercisable (in dollars per share) $ 39.62  
Weighted Average Remaining Contractual Life    
Outstanding, weighted average remaining contractual life (in years) 4 years 8 months 4 years
Exercisable weighted average remaining contractual life (in years) 4 years 1 month  
Aggregate Intrinsic Value    
Beginning balance $ 40,137  
Granted 596  
Exercised 9,741  
Canceled 117  
Ending balance 30,791 $ 40,137
Exercisable $ 29,714