CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1	$ 10
Preferred stock, par value (dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, issued (in shares)	3,677,000	3,672,000
Common stock, shares, outstanding (in shares)	2,690,000	2,685,000
Treasury stock, shares (in shares)	987,000	987,000