| Assets and liabilities of disposal group | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
  | 
      | 
  | 
  | 
    |   | 
  | 
    Three Months
    Ended September 30, | 
  | 
  | 
    Six Months
    Ended September 30, | 
  | 
  
    |   | 
  | 
    2021 | 
  | 
  | 
    2020 | 
  | 
  | 
    2021 | 
  | 
  | 
    2020 | 
  | 
  
    | Revenues | 
  | 
    $ | 
– | 
  | 
  | 
    $ | 
2,000 | 
  | 
  | 
    $ | 
– | 
  | 
  | 
    $ | 
214,000 | 
  | 
  
    | Cost of revenues | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
53,000 | 
  | 
  
    | Selling general and administrative expenses | 
  | 
      | 
– | 
  | 
  | 
      | 
33,000 | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
39,000 | 
  | 
  
    | Income (loss) from discontinued operations before tax | 
  | 
      | 
– | 
  | 
  | 
      | 
(31,000 | 
) | 
  | 
      | 
– | 
  | 
  | 
      | 
122,000 | 
  | 
  
    | Gain on disposal of discontinued operations before income taxes | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
795,000 | 
  | 
  
    | Total income (loss) from discontinued operations, before tax | 
  | 
      | 
– | 
  | 
  | 
      | 
(31,000 | 
) | 
  | 
      | 
– | 
  | 
  | 
      | 
917,000 | 
  | 
  
    | Income tax benefit (expense) | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  | 
      | 
– | 
  | 
  
    | Income (loss) from discontinued operations, net of tax | 
  | 
    $ | 
– | 
  | 
  | 
    $ | 
(31,000 | 
) | 
  | 
    $ | 
– | 
  | 
  | 
    $ | 
917,000 | 
  |