Basis of Presentation - Additional Information (Details)

v3.21.2

Basis of Presentation - Additional Information (Details)													1 Months Ended				3 Months Ended		8 Months Ended	9 Months Ended		12 Months Ended
	Feb. 10, 2021 USD ($) $ / shares shares	Feb. 09, 2021 USD ($) $ / shares shares	Feb. 08, 2021 $ / shares shares	Feb. 03, 2021 $ / shares shares	Nov. 02, 2020 USD ($) $ / shares shares	Oct. 31, 2020 $ / shares shares	Oct. 27, 2020 USD ($) $ / shares shares	Jul. 02, 2020 $ / shares shares	Jun. 05, 2020 $ / shares shares	Jun. 03, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($)	Jan. 21, 2020 USD ($) Debtinstrument $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 30, 2020 USD ($)	Oct. 31, 2020 $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	Jan. 28, 2021 $ / shares	Sep. 08, 2020 USD ($)	Jun. 10, 2020 $ / shares	Jul. 16, 2019 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Description of deferring payment on US payroll taxes																				In April 2020, the Company began deferring payment on its share of U.S. payroll taxes owed, as allowed by the Coronavirus Aid, Relief and Economic Security Act (CARES Act) through December 31, 2020. The Company is able to defer half of its share of U.S. payroll taxes owed until December 31, 2021, with the remaining half due on December 31, 2022.
Ordinary shares, shares issued | shares													49,431,028				182,775,282		182,775,282	182,775,282		49,431,028
Ordinary shares, par value | $ / shares													$ 0.01				$ 0.01		$ 0.01	$ 0.01		$ 0.01	$ 0.01		$ 0.01
Proceeds from registered direct offerings, net of transaction costs																				$ 500,000
Number of warrants to purchase ordinary shares | shares																	380,000		380,000	380,000
Net losses																	$ (3,741,000)	$ 12,199,000		$ 87,382,000	$ 40,820,000	$ 52,006,000
Accumulated deficit													$ 286,929,000				374,311,000		$ 374,311,000	374,311,000		286,929,000
Cash and cash equivalents													14,508,000				35,982,000		35,982,000	35,982,000		14,508,000
Short-term investments																	$ 49,729,000		$ 49,729,000	$ 49,729,000
June 3 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, par value | $ / shares																	$ 0.01		$ 0.01	$ 0.01
June 30 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, par value | $ / shares																	$ 0.01		$ 0.01	$ 0.01
February SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares		17,500,000
Ordinary shares, par value | $ / shares		$ 0.01
Offering price per share | $ / shares		$ 2.00
Aggregate gross proceeds from ordinary shares		$ 35,000,000.0
Proceeds from registered direct offerings, net of transaction costs		$ 32,200,000
Percentage of ordinary shares issued to purchase warrants		7.00%
Offering closing date		Feb. 12, 2021
February SPA | Warrant
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares		1,225,000
Warrants to purchase ordinary shares, exercise price | $ / shares		$ 2.50
Warrants expiry date		Feb. 09, 2026
Iterum Therapeutics US Limited | Silicon Valley Bank (SVB) | Paycheck Protection Program
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount											$ 744,000
Debt instrument interest rate											1.00%
Debt instrument maturity period											2 years
Debt instrument, description											Under the terms of the agreement, there shall be no payments due by the Company until the SBA remits the forgiveness amount to the Borrower or 10 months after the end of the six-month period beginning April 30, 2020 (the Deferral Period). Following the Deferral Period, equal monthly repayments of principal and interest will be due to fully amortize the principal amount outstanding on the PPP loan by the maturity date.									Under the terms of the agreement, there shall be no payments due by the Company until the SBA remits the forgiveness amount to the Borrower or until after the Deferral Period. Following the Deferral Period, equal monthly repayments of principal and interest will be due to fully amortize the principal amount outstanding on the PPP loan by the maturity date.
Debt instrument, forgiveness loan														$ 340,000
Debt instrument, remaining amount amortized													$ 404,000
Maximum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate initial offering price of securities authorized to issue																										$ 150,000,000.0
2025 Exchangeable Notes
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount																	$ 12,600,000		$ 12,600,000	$ 12,600,000
Private Placement and Rights Offering | 2025 Exchangeable Notes
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount												$ 51,800,000
Debt instrument interest rate												6.50%
Private Placement and Rights Offering | RLNs
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount												$ 100,000
Private Placement | June 3 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares									208,023
Warrants to purchase ordinary shares, exercise price | $ / shares									$ 2.1031	$ 1.62
Warrants expiry date									Jun. 03, 2025	Dec. 05, 2025
Warrants closing date										Jun. 05, 2020
Percentage of ordinary shares issued to purchase warrants									7.00%
Private Placement | June 30 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares								236,088
Warrants to purchase ordinary shares, exercise price | $ / shares								$ 1.8531								$ 1.42
Warrants expiry date								Jun. 30, 2025								Jan. 02, 2026
Warrants closing date																Jul. 02, 2020
Percentage of ordinary shares issued to purchase warrants								7.00%
Private Placement | Maximum | June 3 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares										1,485,885
Private Placement | Maximum | June 30 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares																1,686,343
Private Placement | 2025 Exchangeable Notes
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount												51,600,000
Debt instrument price per unit												1,000
Private Placement | RLNs
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount												$ 100,000
Number of debt instruments within each notes | Debtinstrument												50
Debt instrument, aggregate potential payment capped rate												4,000 times
Private Placement | Securities
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Debt instrument, shares embedded within each unit, shares | shares					1,286.1845							1,000
Debt instrument, shares embedded within each unit, value					$ 1,000							$ 1,000
Rights Offering in Connection with Private Placement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Maximum subscription units to be accepted | shares												220
Rights Offering in Connection with Private Placement | 2025 Exchangeable Notes
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount																	$ 12,600,000		12,600,000	$ 12,600,000				$ 200,000
Debt instrument price per unit												$ 1,000
Debt instrument price per unit												$ 1,000
Debt instrument, shares embedded within each unit, shares | shares					1,286.1845							1,000
Debt instrument, shares embedded within each unit, value					$ 1,000							$ 1,000
Debt instrument, shares embedded within each unit, exchange price | $ / shares					$ 0.7775							$ 1.00
Aggregate principal amount of exchangeable notes																			$ 39,200,000
Debt instrument, aggregate number of shares exchanged | shares																			53,888,331
Rights Offering in Connection with Private Placement | RLNs
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aggregate principal amount																								$ 20,000.00
Number of debt instruments within each notes | Debtinstrument												50
Aggregate amount payable per unit												$ 160.00
Debt instrument, aggregate potential payment capped rate												4,000 times
Rights Offering in Connection with Private Placement | RLNs | Minimum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Debt instrument, percentage of net revenue from domestic sale for potential aggregate payments												15.00%
Rights Offering in Connection with Private Placement | RLNs | Maximum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Debt instrument, percentage of net revenue from domestic sale for potential aggregate payments												20.00%
Rights Offering in Connection with Private Placement | Securities
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from sale of securities												$ 45,000,000.0
Direct Offering | June 3 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares										2,971,770
Ordinary shares, par value | $ / shares										$ 0.01
Offering price per share | $ / shares										$ 1.6825
Aggregate gross proceeds from ordinary shares										$ 5,000,000.0
Proceeds from registered direct offerings, net of transaction costs										$ 4,300,000
Direct Offering | June 30 SPA
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares																3,372,686
Ordinary shares, par value | $ / shares																$ 0.01
Offering price per share | $ / shares																$ 1.4825
Aggregate gross proceeds from ordinary shares																$ 5,000,000.0
Proceeds from registered direct offerings, net of transaction costs																$ 4,200,000
October Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares							15,511,537
Ordinary shares, par value | $ / shares							$ 0.01										$ 0.01		$ 0.01	$ 0.01
Aggregate gross proceeds from ordinary shares							$ 17,400,000
Proceeds from registered direct offerings, net of transaction costs							$ 15,500,000													$ 13,900,000
Number of warrants to purchase ordinary shares | shares						1,884,615									1,884,615		20,890,516		20,890,516	20,890,516
Warrants to purchase ordinary shares, exercise price | $ / shares						$ 0.8125	$ 0.65								$ 0.8125
Warrants expiry date						Oct. 22, 2025	Oct. 27, 2025
Percentage of ordinary shares issued to purchase warrants						7.00%
October Offering | Pre-Funded Warrants
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Offering price per share | $ / shares							$ 0.01
Proceeds from registered direct offerings, net of transaction costs																						$ 110,000
Number of warrants to purchase ordinary shares | shares							11,411,539
Warrants to purchase ordinary shares, exercise price | $ / shares							$ 0.64
Percentage of ordinary share at election of purchaser							9.99%
October Offering | Warrant
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Offering price per share | $ / shares							$ 0.65
Number of warrants to purchase ordinary shares | shares							20,192,307
Warrants to purchase ordinary shares, exercise price | $ / shares							$ 0.65
October Offering | Purchase Agreement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares						1,884,615									1,884,615
Warrants to purchase ordinary shares, exercise price | $ / shares						$ 0.8125									$ 0.8125
Warrants expiry date															Oct. 22, 2025
Percentage of ordinary shares issued to purchase warrants															7.00%
Description of purchase agreement																				In connection with the October Offering, the Company entered into a Securities Purchase Agreement (the Purchase Agreement) on October 22, 2020 with certain institutional investors. The Purchase Agreement contains customary representations and warranties of the Company, termination rights of the parties, and certain indemnification obligations of the Company.
October Offering | Minimum | Pre-Funded Warrants
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Percentage of beneficial ownership that certain purchasers didn't want to exceed							4.99%
October Offering | Maximum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares							20,192,307
February Underwritten Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Warrants to purchase ordinary shares, exercise price | $ / shares	$ 1.4375		$ 1.4375
Warrants expiry date	Feb. 03, 2026		Feb. 03, 2026
Percentage of ordinary shares issued to purchase warrants	7.00%		7.00%
Offering closing date	Feb. 10, 2021		Feb. 08, 2021
Additional ordinary shares that can be purchased by underwriter | shares	5,217,391
February Underwritten Offering | Underwriting Agreement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares				34,782,609
Ordinary shares, par value | $ / shares				$ 0.01
Offering price per share | $ / shares				$ 1.15
Offering closing date				Feb. 08, 2021
February Underwritten Offering | Pursuant to the Underwriting Agreement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Ordinary shares, shares issued | shares	40,000,000
Aggregate gross proceeds from ordinary shares	$ 46,000,000.0
Proceeds from registered direct offerings, net of transaction costs	$ 42,100,000
Percentage of ordinary shares issued to purchase warrants	7.00%
Additional ordinary shares that can be purchased by underwriter | shares	5,217,391
February Underwritten Offering | Pursuant to the Underwriting Agreement | Warrant
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares	2,800,000
Warrants to purchase ordinary shares, exercise price | $ / shares	$ 1.4375
Warrants expiry date	Feb. 03, 2026
February Underwritten Offering | Maximum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of warrants to purchase ordinary shares | shares	365,217		2,434,783