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Stock Plans - Summary of Performance Stock Unit Activity (Details) - Performance Stock Unit
9 Months Ended
Sep. 30, 2017
$ / shares
shares
Shares  
Unvested, beginning balance (in shares) | shares 186,621
Granted (in shares) | shares 98,886
Performance adjustments (in shares) | shares 27,915
Vested (in shares) | shares (71,403)
Unvested, ending balance (in shares) | shares 242,019
Weighted Average Exercise Price (dollars per share)  
Unvested, beginning balance (dollars per share) | $ / shares $ 46.18
Granted (dollars per share) | $ / shares 72.73
Performance adjustments (dollars per share) | $ / shares 57.26
Vested (dollars per share) | $ / shares 56.47
Unvested, ending Balance (dollars per share) | $ / shares $ 55.06