Net Loss Per Share - Basic and diluted net loss per share computation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator:
Net loss attributable to CASI Pharmaceuticals, Inc.	$ (7,680)	$ (8,596)	$ (6,946)	$ (13,883)	$ (16,276)	$ (20,829)
Denominator:
Weighted average number of common stock	13,606,130		13,979,636		13,700,282	13,235,128
Denominator for basic and diluted net loss per share calculation	13,606,130		13,979,636		13,700,282	13,235,128
Net loss per share (basic)	$ (0.56)		$ (0.50)		$ (1.19)	$ (1.57)
Net loss per share (diluted)	$ (0.56)		$ (0.50)		$ (1.19)	$ (1.57)