Inventories - Reserve Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Inventory, Reserve [Roll Forward]
Beginning balance	$ (2,956)	$ (3,326)	$ (2,894)	$ (2,894)	$ (3,645)
Accrual	34	(187)		(64)	(75)
Reduction due to sold inventory	36	121		72	288
Write-off for disposed inventory	0	(23)	17	0
Reserves for excess, obsolete, and slow-moving inventories	$ (2,886)	$ (3,415)	$ (2,956)	$ (2,886)	$ (3,415)