Revenues and Trade Receivables, Net, Changes in Allowance for Bad Debt (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts at beginning of year	$ 58	$ 55
Additions charged to bad debt expense	30	53
Write-downs charged against the allowance	0	(50)
Allowance for doubtful accounts at end of the period	$ 88	$ 58