Stock Option Plans - Summary of Option Activity (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Number of Shares
Outstanding at beginning of period (in shares) | shares	833,630
Granted (in shares) | shares	232,500
Exercised (in shares) | shares	(95,166)
Expired/Forfeited (in shares) | shares	(3,750)
Outstanding at end of period (in shares) | shares	967,214
Exercisable at end of period (in shares) | shares	484,839
Weighted Average Exercise Price per share
Outstanding at beginning of period (in usd per share) | $ / shares	$ 49.92
Granted (in usd per share) | $ / shares	59.41
Exercised (in usd per share) | $ / shares	47.03
Expired/Forfeited (in usd per share) | $ / shares	53.73
Outstanding at end of period (in usd per share) | $ / shares	52.47
Exercisable at end of period (in usd per share) | $ / shares	$ 48.70
Aggregate Intrinsic Value
Outstanding at beginning of period | $	$ 13,913,891
Granted | $	581,250
Exercised | $	1,403,256
Expired/Forfeited | $
Outstanding at end of period | $	9,130,494
Exercisable at end of period | $	$ 6,402,577