Stock Options (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Apr. 05, 2012
Stock options under 2012 Plan
Stock option details
Shares available for future grants	2,500		2,500		800,000
Maximum exercisable period for options granted			10 years
Stock option activity
Options outstanding at the beginning of the period (in shares)			668,166
Plus: Options granted (in shares)			229,700
Less:
Options exercised (in shares)			46,351
Options forfeited (in shares)			15,800
Options outstanding at the end of the period (in shares)	835,715		835,715
Options fully vested and exercisable at the end of the period (in shares)	327,341		327,341
Stock Options, Weighted average exercise price
Options outstanding at the beginning, weighted average exercise price (in dollars per share)			$ 20.41
Plus: Options granted, weighted average exercise price (in dollars per share)			38.30
Less:
Options exercised, weighted average exercise price (in dollars per share)			17.50
Options forfeited, weighted average exercise price (in dollars per share)			18.58
Options outstanding at the end, weighted average exercise price (in dollars per share)	$ 25.53		25.53
Options fully vested and exercisable at the end, weighted average exercise price (in dollars per share)	$ 19.64		$ 19.64
Stock Options, Weighted average remaining contractual term (years)
Options outstanding at the end, weighted average remaining contractual term (years)			6 years 5 months 9 days
Options fully vested and exercisable at the end, weighted average remaining contractual term (years)			4 years 6 months 22 days
Stock Options, Aggregate intrinsic value
Options outstanding at the end, aggregate intrinsic value	$ 14,436,000		$ 14,436,000
Options fully vested and exercisable at the end, aggregate intrinsic value	7,582,000		7,582,000
Stock-based compensation expense	285,000	$ 216,000	470,000	$ 484,000
Stock-based compensation cost, unrecognized, related to non-vested options	$ 3,316,000		$ 3,316,000
Stock-based compensation cost, unrecognized, related to non-vested options, weighted-average period of recognition			1 year 10 months 24 days
Incentive stock options granted to 10% shareholders
Stock option details
Maximum exercisable period for options granted			5 years