Revenue - Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Change In Contract With Customer, Liability [Roll Forward]
Beginning balance	$ 1,713	$ 2,375
Revenue recognized that was included in balance at beginning of the year	(1,477)	(1,380)
Deferred revenue, net, related to contracts entered into during the year	1,248	718
ATRM beginning balance	317
Ending balance	$ 1,801	$ 1,713