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Stock Plans - Summary of Stock Option Activity (Details)
 9 Months Ended
Sep. 30, 2017
$ / shares
shares
Shares  
Outstanding, beginning balance (in shares) | shares 1,576,092
Exercised (in shares) | shares (422,711)
Outstanding, ending balance (in shares) | shares 1,153,381
Exercisable (in shares) | shares 785,377
Weighted Average Exercise Price (dollars per share)  
Outstanding, beginning balance (dollars per share) | $ / shares $ 37.63
Exercised (dollars per share) | $ / shares 29.32
Outstanding, ending balance (dollars per share) | $ / shares 40.68
Exercisable (dollars per share) | $ / shares $ 38.11