Employee Benefit Plans - Stock Transactions - Stock Option Plans (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Shares
Options Outstanding, beginning shares			504,573
Options granted, shares	0	0	114,500	47,100
Options exercised, shares	(22,600)	(29,618)	(77,607)	(46,682)
Options forfeited, shares			(7,433)
Options expired, shares			0
Options Outstanding, ending shares	534,033		534,033		504,573
Shares Exercisable	335,072		335,072
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)			5.05
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)	11.24		11.24		$ 8.31
Weighted average exercise price, Options Exercisable (in dollars per share)	$ 7.72		$ 7.72
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 3 months 18 days
Aggregate intrinsic value: Options Outstanding	$ 6,146,335		$ 6,146,335		$ 5,772,843
Aggregate intrinsic value, Options exercisable	$ 5,035,701		$ 5,035,701