Description of the business and recent developments: Allowance for credit losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Description of the business and recent developments:
Balance at Beginning of Period	$ 1,457	$ 1,976	$ 1,921	$ 1,771
Current-period Provision for Expected Credit Losses	1,187	1,432	3,199	2,768
Write offs Charged Against Allowance	(971)	(1,293)	(3,447)	(2,424)
Balance at End of Period	1,673	2,115	1,673	2,115
Bad debt recoveries	$ 400	$ 200	$ 1,600	$ 400