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Stock Plans - Summary of Restricted Stock and Unit Activity (Details) - Restricted Stock Activity
6 Months Ended
Jun. 30, 2017
$ / shares
shares
Shares  
Unvested, beginning balance (in shares) | shares 234,592
Granted (in shares) | shares 49,189
Vested (in shares) | shares (71,628)
Forfeited (in shares) | shares (3,174)
Unvested, ending balance (in shares) | shares 208,979
Weighted Average Exercise Price (dollars per share)  
Unvested, beginning balance (dollars per share) | $ / shares $ 49.76
Granted (dollars per share) | $ / shares 73.92
Vested (dollars per share) | $ / shares 51.32
Forfeited (dollars per share) | $ / shares 50.11
Unvested, ending Balance (dollars per share) | $ / shares $ 55.53