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Stock Option Plans - Summary of Option Activity (Details)
 6 Months Ended
Jun. 30, 2016
USD ($)
$ / shares
shares
Number of Shares  
Outstanding at beginning of period (in shares) | shares 860,274
Granted (in shares) | shares 226,500
Exercised (in shares) | shares (169,732)
Expired/Forfeited (in shares) | shares (2,500)
Outstanding at end of period (in shares) | shares 914,542
Exercisable at end of period (in shares) | shares 452,417
Weighted Average Exercise Price per share  
Outstanding at beginning of period (in usd per share) | $ / shares $ 46.58
Granted (in usd per share) | $ / shares 57.74
Exercised (in usd per share) | $ / shares 45.76
Expired/Forfeited (in usd per share) | $ / shares 40.35
Outstanding at end of period (in usd per share) | $ / shares 49.52
Exercisable at end of period (in usd per share) | $ / shares $ 46.43
Aggregate Intrinsic Value  
Outstanding at beginning of period | $ $ 4,237,456
Granted | $ 899,205
Exercised | $ 1,878,685
Expired/Forfeited | $
Outstanding at end of period | $ 11,151,610
Exercisable at end of period | $ $ 6,915,024