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Stock Plans - Summary of Restricted Stock and Unit Activity (Details) - Restricted Stock Activity
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Shares  
Unvested, beginning balance (in shares) | shares 227,161
Granted (in shares) | shares 49,111
Vested (in shares) | shares (50,075)
Forfeited (in shares) | shares (2,804)
Unvested, ending balance (in shares) | shares 223,393
Weighted Average Exercise Price (dollars per share)  
Unvested, beginning balance (dollars per share) | $ / shares $ 57.50
Granted (dollars per share) | $ / shares 83.60
Vested (dollars per share) | $ / shares 52.23
Forfeited (dollars per share) | $ / shares 55.26
Unvested, ending Balance (dollars per share) | $ / shares $ 64.92