Allowance for Doubtful Accounts Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts
Balance, beginning of year	$ 1,748	$ 1,957	$ 1,829
Provision (net of recovery)	2,090	907	370
Amounts written off, net of recoveries	(389)	(1,116)	(242)
Balance, end of year	$ 3,449	$ 1,748	$ 1,957