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Stock Plans - Summary of Performance Stock Unit Activity (Details) - Performance Stock Unit
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Shares  
Unvested, beginning balance (in shares) | shares 218,886
Granted (in shares) | shares 76,813
Performance adjustments (in shares) | shares 77,783
Vested (in shares) | shares (139,476)
Unvested, ending balance (in shares) | shares 234,006
Weighted Average Exercise Price (dollars per share)  
Unvested, beginning balance (dollars per share) | $ / shares $ 68.43
Granted (dollars per share) | $ / shares 100.66
Performance adjustments (dollars per share) | $ / shares 43.77
Vested (dollars per share) | $ / shares 44.75
Unvested, ending Balance (dollars per share) | $ / shares $ 84.93