Inventories - Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for excess and obsolete inventories:
Balance, beginning of period	$ 2,644	$ 1,210	$ 1,118
Provisions for excess and obsolete inventories	1,108	1,454	152
Inventories written off	(491)	(20)	(60)
Balance, end of period	$ 3,261	$ 2,644	$ 1,210