Stock option and award plan: Incentive award plan - activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock option activity parenthetical
Proceeds from exercises of common stock options	$ 1,823	$ 1,382	$ 1,637
Stock options
Stock option activity
Outstanding at the beginning of the period (in shares)	159,880
Granted (in shares)	76,768
Cancelled and expired (in shares)	(51,645)
Exercised (in shares)	(36,468)
Outstanding at the end of the period (in shares)	148,535	159,880
Exercisable at the end of the period (in shares)	89,904
Expected to vest (in shares)	131,701
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 54.09
Granted (in dollars per share)	69.54
Cancelled and expired (in dollars per share)	68.00
Exercised (in dollars per share)	50.00
Outstanding at the end of the period (in dollars per share)	58.24	$ 54.09
Exercisable at the end of the period (in dollars per share)	50.70
Expected to vest (in dollars per share)	$ 56.55
Stock option activity parenthetical
Exercised - intrinsic value	$ 900
Proceeds from exercises of common stock options	1,800
Outstanding end of period - intrinsic value	$ 2,400
Outstanding - weighted-average term	6 years 10 months 24 days
Exercisable - intrinsic value	$ 2,100
Exercisable - weighted average term	5 years 6 months
Expected to vest - intrinsic value	$ 2,300
Expected to vest - weighted average term	6 years 7 months 6 days