Significant Accounting Policies - Additional Information (Details)			3 Months Ended					12 Months Ended
	Nov. 08, 2019 USD ($)	Oct. 07, 2016 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) Obligation	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Operating lease Right-of-Use assets								$ 3,735,000				$ 3,022,000
Operating lease liabilities								$ 4,189,000
Number of performance obligation | Obligation								2
Upfront fee allocated to license component								$ 17,500,000
Revenues			$ 18,000	$ 283,000	$ 364,000	$ 481,000		18,000	$ 1,128,000	$ 8,158,000
Agenus Agreement
Summary Of Significant Accounting Policy [Line Items]
Upfront fee	$ 10,000,000.0
Maximum amount payable upon achieving certain clinical development and regulatory milestones	115,000,000.0
Maximum amount payable upon achieving certain commercial milestones	$ 85,000,000.0
Agenus Agreement | Minimum
Summary Of Significant Accounting Policy [Line Items]
Royalty ranging on net sales of licensed products	14.00%
Agenus Agreement | Maximum
Summary Of Significant Accounting Policy [Line Items]
Royalty ranging on net sales of licensed products	20.00%
Allergan
Summary Of Significant Accounting Policy [Line Items]
Consideration received for license and future supply services		$ 17,500,000									$ 17,500,000
Milestone payment for licensing agreement							$ 7,500,000			7,500,000
Revenues								$ 18,000	$ 1,100,000	$ 700,000
Type Of Revenue Extensible List								urgn:RTGelMember	urgn:RTGelMember	urgn:RTGelMember
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policy [Line Items]
Operating lease Right-of-Use assets												3,700,000
Operating lease liabilities												$ 4,200,000