Stock incentive plans - Stock option awards (Details) - Stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Number of Options
Outstanding at beginning of period (in shares)	235
Exercised (in shares)	(63)
Canceled/forfeited (in shares)	(21)
Outstanding and exercisable at end of period (in shares)	151	235
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 7.67
Exercised (in dollars per share)	7.03
Canceled/forfeited (in dollars per share)	12.15
Outstanding and exercisable at end of period (in dollars per share)	$ 7.33	$ 7.67
Weighted-Average Remaining Contract Life (years)
Outstanding and exercisable at end of period	2 years 3 months 18 days	2 years 7 months 6 days
Aggregate Intrinsic Value
Outstanding and exercisable at end of period	$ 501	$ 870