Fair value measurements (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Financial assets:
Cash and cash equivalents	$ 361	$ 358
Warrants, fair value	99	103	$ 77	$ 77
Financial liabilities:
Non-recourse debt	280	295
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	361	358
Warrants, fair value	99	103
Financial liabilities:
Non-recourse debt	287	305
Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents	361	358
Warrants, fair value	0	0
Financial liabilities:
Non-recourse debt	0	0
Fair Value, Inputs, Level 2 [Member]
Financial assets:
Cash and cash equivalents	0	0
Warrants, fair value	0	0
Financial liabilities:
Non-recourse debt	0	0
Fair Value, Inputs, Level 3 [Member]
Financial assets:
Cash and cash equivalents	0	0
Warrants, fair value	99	103
Financial liabilities:
Non-recourse debt	$ 280	$ 295