Net Loss Per Share of Common Stock - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Basic and diluted net loss per share of common stock:
Net loss attributable to Onconova Therapeutics, Inc.	$ (20,573)	$ (24,092)
Weighted average shares of common stock outstanding (in shares)	4,124,073	600,022
Net loss per share of common stock-basic and diluted	$ (4.99)	$ (40.15)