Summary of Significant Accounting Policies - Receivables and Allowances for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables and Allowances for Doubtful Accounts
Balances at Beginning of Year	$ 39	$ 137	$ 781
Net charges to bad debt expense	1,183	464	426
Recoveries	(81)	(562)
Write-offs	(152)		(1,070)
Balances at End of Year	$ 989	$ 39	$ 137