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Stock Plans - Summary of Performance Stock Unit Activity (Details) - Performance Stock Unit
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Shares  
Unvested, beginning balance (in shares) | shares 242,186
Granted (in shares) | shares 62,775
Performance adjustments (in shares) | shares (3,356)
Vested (in shares) | shares (41,660)
Unvested, ending balance (in shares) | shares 251,286
Weighted Average Exercise Price (dollars per share)  
Unvested, beginning balance (dollars per share) | $ / shares $ 55.06
Granted (dollars per share) | $ / shares 84.79
Performance adjustments (dollars per share) | $ / shares 44.61
Vested (dollars per share) | $ / shares 40.23
Unvested, ending Balance (dollars per share) | $ / shares $ 65.45
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period | shares 8,659
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares $ 44.53