Stock Compensation Plans - Stock option activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Stock Compensation Plans
Options Outstanding, January 1, 2019 | shares	39,400
Options Outstanding, Forfeited or cancelled | shares	0
Options Outstanding, Exercised | shares	(19,200)
Options Outstanding, Granted | shares	0
Options outstanding, September 30, 2019 | shares	20,200
Vested or expected to vest at September 30, 2019 | shares	20,200
Exercisable at September 30, 2019 | shares	14,500
Weighted Average Exercise Price, Outstanding, January 1, 2019 | $ / shares	$ 14.00
Weighted Average Exercise Price, Forfeited or cancelled | $ / shares	0
Weighted Average Exercise Price, Exercised | $ / shares	10.15
Weighted Average Exercise Price, Granted | $ / shares	0
Weighted Average Exercise Price, outstanding, September 30, 2019 | $ / shares	17.66
Weighted Average Exercise Price, Vested or expected to vest at September 30, 2019 | $ / shares	17.66
Weighted Average Exercise Price, Exercisable at September 30, 2019 | $ / shares	$ 17.48
Weighted Average Remaining Contractual Term (in years), outstanding, September 30, 2019	5 years 7 days
Weighted Average Remaining Contractual Term (in years), Vested or expected to vest at September 30, 2019	5 years 7 days
Weighted Average Remaining Contractual Term (in years), Exercisable at September 30, 2019	4 years 8 months 12 days
Aggregate Intrinsic Value, outstanding, September 30, 2019 | $	$ 228
Aggregate Intrinsic Value, Vested or expected to vest at September 30, 2019 | $	228
Aggregate Intrinsic Value, Exercisable at September 30, 2019 | $	$ 166