Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets, Current [Abstract]
Cash and cash equivalents	$ 1,116	$ 1,102
Treasury bills	5,427	5,248
Available-for-sale securities	2,640	3,677
Trade receivables, less allowance for doubtful accounts of $8 and $10, respectively	730	602
Inventories	1,260	1,330
Other current assets	158	75
Total current assets	11,331	12,034
Property and equipment, net	1,240	1,304
Total assets	12,571	13,338
Liabilities, Current [Abstract]
Accounts payable	96	94
Accrued expenses	374	227
Accrued income tax	24	313
Total current liabilities	494	634
Deferred income tax liability	1,042	1,455
Commitments and contingencies
Stockholders' equity
Common stock par value $0.10 per share; authorized 10,000,000 shares; issued and outstanding: 3,394,707 and 3,391,912 shares, respectively	339	339
Additional paid-in capital	1,732	1,575
Retained earnings	7,381	7,113
Accumulated other comprehensive income (unrealized gain on available-for-sale securities, net of income tax)	1,583	2,222
Total stockholders' equity	11,035	11,249
Total liabilities and stockholders' equity	$ 12,571	$ 13,338