Stock Option Plans - Summary of Option Activity (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2007
Number of Shares
Outstanding at beginning of period (in shares)	748,208
Granted (in shares)	225,000	73,403
Exercised (in shares)	(72,309)
Expired/Forfeited (in shares)	0
Outstanding at end of period (in shares)	900,899
Exercisable at end of period (in shares)	476,524
Weighted Average Exercise Price per share
Outstanding at beginning of period (in usd per share)	$ 44.79
Granted (in usd per share)	51.07
Exercised (in usd per share)	42.71
Expired/Forfeited (in usd per share)	0.00
Outstanding at end of period (in usd per share)	46.53
Exercisable at end of period (in usd per share)	$ 45.33
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 9,274,028
Granted	153,000
Exercised	$ 1,041,624
Expired/Forfeited
Outstanding at end of period	$ 4,881,029
Exercisable at end of period	$ 3,235,179