CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets
Accounts receivable, allowance for credit loss, current	$ 116	$ 308
Inventory valuation reserves	849	851
Accumulated depreciation, depletion and amortization, property, plant and equipment	$ 33,805	$ 32,057
Stockholders’ equity
Common stock, par or stated value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	66,755,230	64,625,071
Common stock, shares outstanding (in shares)	66,755,230	64,625,071