Nature of the Business - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Dec. 19, 2017 $ / shares shares	Jan. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Disease Novel $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of rare diseases | Disease			1,800
Number of novel ERSG drug candidates | Novel			170
Common stock, par value | $ / shares			$ 0.01	$ 0.01
Accumulated deficit			$ (86,145)	$ (38,960)
Cash and cash equivalents			$ 48,606	$ 24,049	$ 2,212
Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from a debt issuance		$ 14,800
Eloxx Limited [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Common stock, par value | $ / shares	$ 0.01
Issuance of shares in exchange of all outstanding capital stock | shares	20,316,656
Reverse stock split	0.05