| Schedule of marketable securities | 
  
    | Schedule of marketable securities | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
 
    |   | 
  | 
    June
    30, 2023 | 
  | 
 
  
    |   | 
  | 
    Cost  Basis  | 
  | 
  | 
    Gross 
Unrealized 
Gains  | 
  | 
  | 
    Gross 
Unrealized 
Losses  | 
  | 
  | 
    Fair Value  | 
  | 
 
  
    |   | 
  | 
      | 
  | 
  | 
      | 
  | 
  | 
      | 
  | 
  | 
      | 
  | 
 
  
    | Certificates of deposit | 
  | 
    $ | 
5,250,000 | 
  | 
  | 
    $ | 
— | 
  | 
  | 
    $ | 
(30,000 | 
) | 
  | 
    $ | 
5,220,000 | 
  | 
 
  
    | Government securities | 
  | 
      | 
16,631,000 | 
  | 
  | 
      | 
236,000 | 
  | 
  | 
      | 
(35,000 | 
) | 
  | 
      | 
16,832,000 | 
  | 
 
  
    | Fixed income mutual funds | 
  | 
      | 
7,650,000 | 
  | 
  | 
      | 
— | 
  | 
  | 
      | 
(126,000 | 
) | 
  | 
      | 
7,524,000 | 
  | 
 
  
    | Corporate bond | 
  | 
      | 
193,000 | 
  | 
  | 
      | 
— | 
  | 
  | 
      | 
(14,000 | 
) | 
  | 
      | 
179,000 | 
  | 
 
  
    | Total marketable securities | 
  | 
    $ | 
29,724,000 | 
  | 
  | 
    $ | 
236,000 | 
  | 
  | 
    $ | 
(205,000 | 
) | 
  | 
    $ | 
29,755,000 | 
  | 
 
  
    |   | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
 
   
  
  
    |   | 
  | 
    December
    31, 2022 | 
  | 
 
  
    |   | 
  | 
    Cost  Basis  | 
  | 
  | 
    Gross 
Unrealized 
Gains  | 
  | 
  | 
    Gross 
Unrealized 
Losses  | 
  | 
  | 
    Fair Value  | 
  | 
 
  
    |   | 
  | 
      | 
  | 
  | 
      | 
  | 
  | 
      | 
  | 
  | 
      | 
  | 
 
  
    | Government Securities | 
  | 
    $ | 
20,781,000 | 
  | 
  | 
    $ | 
67,000 | 
  | 
  | 
    $ | 
— | 
  | 
  | 
    $ | 
20,848,000 | 
  | 
 
  
    | Fixed income mutual funds | 
  | 
      | 
11,904,000 | 
  | 
  | 
      | 
— | 
  | 
  | 
      | 
(915,000 | 
) | 
  | 
      | 
10,989,000 | 
  | 
 
  
    | Certificates of Deposit | 
  | 
      | 
3,019,000 | 
  | 
  | 
      | 
— | 
  | 
  | 
      | 
(43,000 | 
) | 
  | 
      | 
2,976,000 | 
  | 
 
  
    | Corporate bonds and notes | 
  | 
      | 
192,000 | 
  | 
  | 
      | 
— | 
  | 
  | 
      | 
(14,000 | 
) | 
  | 
      | 
178,000 | 
  | 
 
  
    | Total marketable securities | 
  | 
    $ | 
35,896,000 | 
  | 
  | 
    $ | 
67,000 | 
  | 
  | 
    $ | 
(972,000 | 
) | 
  | 
    $ | 
34,991,000 | 
  | 
 
   
  
 |