Revenue - Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change In Contract With Customer, Liability [Roll Forward]
Beginning balance	$ 1,801	$ 1,713
ATRM beginning balance (1)		317
Revenue recognized that was included in balance at beginning of the year	(1,494)	(1,477)
Deferred revenue, net, related to contracts entered into during the year	2,045	1,248
Ending balance	$ 2,352	$ 1,801