Accounts Receivable and Allowance for Credit Losses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accounts Receivable and Allowance for Credit Losses
Accounts receivable due maximum period	60 days
Unbilled revenue	$ 4,200		$ 7,400
Allowance for credit losses, beginning	300
Credit losses	2,880	$ 0
Less writeoffs	(2,100)
Allowance for credit losses, ending	$ 1,100