Mustang Bio, Inc. Annual report pursuant to Section 13 and 15(d)

License, Clinical Trial and Sponsored Research Agreements (City of Hope - Sponsored Research and Clinical Trial Agreements) (Narrative) (Details)

License, Clinical Trial and Sponsored Research Agreements (City of Hope - Sponsored Research and Clinical Trial Agreements) (Narrative) (Details)		1 Months Ended				12 Months Ended
	Jan. 03, 2018 USD ($)	Oct. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Feb. 28, 2017 USD ($)	Mar. 31, 2015 USD ($) item	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense						$ 37,237,000	$ 30,042,000
Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense						7,717,000	6,143,000
Sponsored Research and Clinical Trial Agreements [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable					$ 2,000,000.0
Number of installments \| item					4
Research and development expense						500,000	2,000,000
Sponsored Research and Clinical Trial Agreements [Member] \| CD123 Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees paid				$ 19,450
Milestones payable				200,000
Contribution per patient				$ 97,490
Research and development expense						433,000	1,202,000
Agreement term				3 years
Sponsored Research and Clinical Trial Agreements [Member] \| IL13Ra2 Product [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual maintenance fee payable		$ 200,000
Upfront fees paid		29,000		$ 9,300
Milestones payable				200,000
Contribution toward patient costs				$ 100,000
Contribution per patient		100,000
Research and development expense						530,000	876,000
Agreement term				3 years
Sponsored Research and Clinical Trial Agreements [Member] \| CS1 Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense						885,000	0
Sponsored Research and Clinical Trial Agreements [Member] \| CS1 Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable			$ 2,400,000
Sponsored Research and Clinical Trial Agreements [Member] \| HER2 Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable		29,375
Research and development expense						1,519,000	0
Sponsored Research and Clinical Trial Agreements [Member] \| HER2 Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable		3,000,000.0
Sponsored Research and Clinical Trial Agreements [Member] \| PSCA Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable		33,000
Research and development expense						204,000	0
Sponsored Research and Clinical Trial Agreements [Member] \| PSCA Product or Process [Member] \| City of Hope National Medical Center ("COH") [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable		$ 2,300,000
Sponsored Research and Clinical Trial Agreements [Member] \| Manufacturing [Member] \| City of Hope National Medical Center ("COH") [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payable	$ 900,000
Research and development expense						$ 0	$ 457,000
Agreement term	2 years