Common stock (Options outstanding) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Options vested and expected to vest (Number of options)	606,327
Options vested and expected to vest (Wtd avg exercise price)	$ 13.41
Options vested and expected to vest (Wtd avg remaining contractual term)	3 years 7 months 13 days
Options vested and expected to vest (Aggregate intrinsic value)	$ 4,566
Options vested and exercisable (Number of options)	606,327
Options vested and exercisable (Wtd avg exercise price)	$ 13.41
Options vested and exercisable (Wtd avg remaining contractual term)	3 years 7 months 13 days
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, Beginning balance	797,501
Options granted	0
Options exercised	(187,174)
Number of Options, Outstanding, Ending balance	606,327	797,501
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 13.31
Wtd Avg Remaining Contractual Term, Options Outstanding	3 years 7 months 13 days	4 years 8 months 15 days
Options granted	$ 0
Options exercised	13.03
Weighted Average Exercise Price, Outstanding, Ending balance	$ 13.41	$ 13.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	4,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 10.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]
Aggregate Intrinsic Value, Options Outstanding	$ 4,566	$ 20,767