Per Share Amounts - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income (loss) attributable to American Shared Hospital Services	$ 29	$ (135)
Weighted average common shares for basic earnings per share (in shares)	6,254	6,126
Diluted effect of stock options and restricted stock (in shares)	68	27
Weighted average common shares for diluted earnings per share (in shares)	6,322	6,153
Basic earnings (loss) per share (in USD per share)	$ 0.00	$ (0.02)
Diluted earnings (loss) per share (in USD per share)	$ 0.00	$ (0.02)