Description of the business and recent developments: Allowance for credit losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Description of the business and recent developments:
Balance at Beginning of Period	$ 1,673	$ 2,115	$ 1,921	$ 1,771
Current-period Provision for Expected Credit Losses	1,340	1,174	4,539	3,942
Write offs Charged Against Allowance	(1,600)	(1,085)	(5,047)	(3,509)
Balance at End of Period	1,413	2,204	1,413	2,204
Bad debt recoveries	$ 300	$ 400	$ 1,900	$ 800