CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Accounts receivable, allowance	$ 28	$ 19
Notes receivable, allowance	8	9
Notes and other receivables, long-term, allowance	$ 4	$ 9
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	10,957,000	10,933,000
Common stock, shares outstanding	10,957,000	10,933,000