Stock Option Plans - Summary of Option Activity (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2007
Number of Shares
Outstanding at beginning of period (in shares)	860,274
Granted (in shares)	0	70,903
Exercised (in shares)	(14,375)
Expired/Forfeited (in shares)	0
Outstanding at end of period (in shares)	845,899
Exercisable at end of period (in shares)	421,524
Weighted Average Exercise Price per share
Outstanding at beginning of period (in usd per share)	$ 46.58
Granted (in usd per share)	0.00
Exercised (in usd per share)	42.00
Expired/Forfeited (in usd per share)	0.00
Outstanding at end of period (in usd per share)	46.66
Exercisable at end of period (in usd per share)	$ 45.44
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 4,237,456
Granted	0
Exercised	$ 139,494
Expired/Forfeited
Outstanding at end of period	$ 5,460,449
Exercisable at end of period	$ 3,275,643