Employee Benefit Plans - Stock Transactions - Stock Option Plans (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Shares
Options Outstanding, beginning shares			504,573
Options granted, shares	0	0	114,500	47,100
Options exercised, shares	(23,366)	(18,480)	(100,973)	(65,162)
Options forfeited, shares			(7,433)
Options expired, shares			0
Options Outstanding, ending shares	510,667		510,667		504,573
Shares Exercisable	311,706		311,706
Weighted average exercise price
Weighted average exercise price, Options Outstanding, beginning (in dollars per share)			$ 8.31
Weighted average exercise price, Options granted (in dollars per share)	$ 0.00	$ 0.00	20.24	$ 16.37
Weighted average exercise price, Options exercised (in dollars per share)			4.95
Weighted average exercise price, Options forfeited (in dollars per share)			15.47
Weighted average exercise price, Options expired (in dollars per share)			0.00
Weighted average exercise price, Options Outstanding, ending (in dollars per share)	11.54		11.54		$ 8.31
Weighted average exercise price, Options Exercisable (in dollars per share)	$ 7.95		$ 7.95
Weighted average remaining contractual life , Options Outstanding			6 years 8 months 12 days		5 years 8 months 12 days
Weighted average remaining contractual life, Options exercisable			5 years 4 months 24 days
Aggregate intrinsic value: Options Outstanding	$ 5,799,514		$ 5,799,514		$ 5,772,843
Aggregate intrinsic value, Options exercisable	$ 4,659,036		$ 4,659,036