Per Share Amounts - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net (loss) income attributable to American Shared Hospital Services	$ (209)	$ 165	$ (827)	$ 466
Weighted average common shares for basic earnings per share (in shares)	6,049	5,889	6,060	5,899
Diluted effect of stock options and restricted stock (in shares)	0	19	0	18
Weighted average common shares for diluted earnings per share (in shares)	6,049	5,908	6,060	5,917
Basic (loss) earnings per share (in USD per share)	$ (0.03)	$ 0.03	$ (0.14)	$ 0.08
Diluted (loss) earnings per share (in USD per share)	$ (0.03)	$ 0.03	$ (0.14)	$ 0.08