Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Details)

v3.20.2
Stockholders' Equity - Additional Information (Details)
 1 Months Ended 3 Months Ended 9 Months Ended
Aug. 29, 2020
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$ / shares
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Aug. 28, 2020
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$ / shares
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Aug. 27, 2020
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shares
Aug. 26, 2020
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$ / shares
shares
May 29, 2020
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$ / shares
shares
Feb. 14, 2020
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$ / shares
shares
Sep. 30, 2020
USD ($)
$ / shares
shares
Jun. 30, 2020
USD ($)
$ / shares
shares
Sep. 30, 2020
USD ($)
$ / shares
shares
Sep. 30, 2019
USD ($)
$ / shares
shares
Sep. 30, 2020
USD ($)
$ / shares
shares
Sep. 30, 2019
USD ($)
$ / shares
shares
Jun. 29, 2020
shares
May 31, 2020
USD ($)
Mar. 23, 2020
USD ($)
Dec. 31, 2019
$ / shares
shares
Aug. 16, 2019
USD ($)
Jun. 17, 2019
$ / shares
shares
Jun. 16, 2019
shares
Jul. 13, 2018
USD ($)
Nov. 30, 2017
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Stock-based compensation expense                 $ 3,171,000 $ 3,741,000 $ 10,319,000 $ 10,423,000                  
Proceeds from issuance of Series A preferred stock                     39,075,000 0                  
Proceeds From Issuance Of Preferred Stock, At The Market Offering                     $ 0 539,000                  
Preferred Stock, Liquidation Preference Per Share | $ / shares             $ 25.00   $ 25.00   $ 25.00         $ 25.00          
Interest Rate             2.50%   2.50%   2.50%                    
Common Stock, Shares, Issued | shares             93,748,374   93,748,374   93,748,374         74,027,425   150,000,000 50,000,000    
Common Stock, Par or Stated Value Per Share | $ / shares             $ 0.001   $ 0.001   $ 0.001         $ 0.001   $ 0.001      
Underwriting discounts and commissions and offering expenses                     $ 3,407,000 0                  
Stock Repurchase Program, Authorized Amount                           $ 5,000,000.0 $ 5,000,000.0            
Preferred shares repurchased and held in treasury | shares             5,000   5,000   5,000                    
Consideration for repurchase of preferred shares                     $ 70,000 0                  
Fees incurred for repurchase of preferred shares                     $ 2,000 0                  
Stock Incentive Plan 2013 [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Common Stock, Shares, Issued | shares               13,000,000.0         3,000,000.0                
Common Stock, Remaining Number of Shares | shares                     4,200,000                    
Research and Development Expense [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Stock-based compensation expense                 $ 700,000 1,200,000 $ 2,500,000 2,600,000                  
General and Administrative Expense [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Stock-based compensation expense                 $ 2,500,000 $ 2,500,000 $ 7,800,000 $ 7,800,000                  
Maximum [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Capital Units, Authorized | shares             150,000,000   150,000,000   150,000,000                    
Minimum [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Capital Units, Authorized | shares             50,000,000   50,000,000   50,000,000                    
2020 Shelf                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Common Stock Shares Available For Future Issuance Value             $ 29,500,000   $ 29,500,000   $ 29,500,000                    
Common Stock [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Common Stock issued in connection with the first ESPP offering | shares                     53,268 54,221                  
Issuance of Common Stock for At the Market Offering in shares | shares                 7,064,214 1,213,643 16,378,234 8,604,469                  
Common Stock [Member] | Market Offering [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Average Price Per Share | $ / shares                     $ 2.74                    
Proceeds From Issuance Of Preferred Stock, At The Market Offering                     $ 44,800,000                    
Issuance of Common Stock for At the Market Offering in shares | shares                     16,400,000                    
Payments for Commissions                     $ 1,600,000                    
Underwriting discounts and commissions and offering expenses         $ 1,100,000 $ 1,300,000                              
Preferred Stock [Member] | Market Offering [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Average Price Per Share | $ / shares         $ 18.00 $ 20.00                              
Preferred Stock [Member] | 2018 Preferred ATM                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Gross proceeds         $ 11,500,000 $ 14,400,000                              
Preferred Stock [Member] | Over-Allotment Option [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares   64,600                                      
Preferred Stock [Member] | IPO [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Shares Issued, Price Per Share | $ / shares   $ 25.00                                      
Average Price Per Share | $ / shares       $ 18.00                                  
Issuance Of Preferred Stock For Public Offering | shares   255,400   666,666 555,556 625,000                              
Preferred Stock dividends Per Share Cash Paid | $ / shares   $ 0.19531                 $ 0.19531                    
Annual dividend | $ / shares   2.34375                                      
Preferred Stock, Liquidation Preference Per Share | $ / shares   $ 25.00                                      
Preferred stock exchange term optional   24 months                                      
Initial dividend paid                     $ 49,883,000                    
Preferred Stock, Dividend Rate, Percentage       9.375% 9.375%                                
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares       66,666 83,333 93,750                              
Interest Rate   9.375%                                      
Gross proceeds   $ 8,000,000.0   $ 13,200,000                                  
Underwriting discounts and commissions and offering expenses   $ 900,000   $ 1,100,000                                  
Mustang Bio, Inc [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Share Price | $ / shares             $ 3.56   $ 3.56 $ 6.42 $ 3.56 $ 6.42                  
Common Stock Shares Available For Future Issuance Value             $ 32,600,000   $ 32,600,000   $ 32,600,000                    
Marketable Securities                                 $ 75,000,000.0     $ 75,000,000.0  
Mustang Bio, Inc [Member] | Common Stock [Member] | Market Offering [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Average Price Per Share | $ / shares               $ 3.25     $ 3.56 $ 6.42                  
Proceeds from issuance of Common stock               $ 37,200,000     $ 25,600,000 $ 22,500,000                  
Proceeds From Issuance Of Common Stock Net of Issuance Costs               $ 34,900,000     $ 25,100,000 $ 22,000,000.0                  
Stock Issued During Period, Shares, New Issues | shares               11,455,604                          
Issuance of Common Stock for At the Market Offering in shares | shares                     7,200,000 3,500,000                  
Agents Commission, Percentage                     3.00%                    
Underwriting discounts and commissions and offering expenses               $ 2,300,000                          
Mustang Bio, Inc [Member] | Common Stock [Member] | Market Offering [Member] | Founders Agreement                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Issuance of Common Stock for At the Market Offering in shares | shares                     117,405 87,656                  
Checkpoint [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Common Stock, Capital Shares Reserved for Future Issuance | shares             12,300,000   12,300,000   12,300,000                    
Marketable Securities                                         $ 100,000,000
Checkpoint [Member] | Common Stock [Member] | Market Offering [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Average Price Per Share | $ / shares             $ 2.80       $ 2.40                    
Proceeds from issuance of Common stock             $ 20,500,000       $ 8,700,000                    
Proceeds From Issuance Of Common Stock Net of Issuance Costs             $ 18,900,000       $ 8,400,000                    
Stock Issued During Period, Shares, New Issues | shares             7,321,429       3,614,344                    
Agents Commission, Percentage                     3.00%                    
Underwriting discounts and commissions and offering expenses             $ 1,600,000                            
Checkpoint [Member] | Common Stock [Member] | Market Offering [Member] | Founders Agreement                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Weighted average price per share | $ / shares                     $ 2.92                    
Stock Issued During Period, Shares, New Issues | shares                     273,379                    
Oaktree Warrants [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares 1,749,450   1,749,450                                    
Purchase price | $ / shares $ 3.20                                        
Percentage of market price 95.00%                                        
Volatility rate 0.868%                                        
Interest Rate 0.74%                                        
Outstanding warrants | shares 4,800,000                                        
Number of Financial instruments | item 2                                        
Fair Value of Warrants     $ 4,400,000               $ 4,400,000                    
Warrant expiration term 10 years                                        
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares $ 3.20                                        
Restricted Stock [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition                     3 years 10 months 24 days                    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options             $ 17,500,000   $ 17,500,000   $ 17,500,000                    
Restricted Stock Units (RSUs) [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition                       5 years                  
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options                   $ 12,700,000   $ 12,700,000                  
Restricted Stock Units (RSUs) [Member] | Mustang Bio, Inc [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Adjustments To Additional Paid In Capital At Market Offering Costs                     $ 500,000 500,000                  
Options to Purchase Common Stock [Member] | Employee Stock [Member]                                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                          
Employee Stock Purchase Plan to eligible employees, Reckoning fair value percentage during offering period             85.00%   85.00%   85.00%                    
Common Stock issued in connection with the first ESPP offering | shares                     507,783                    
Common Stock, Capital Shares Reserved for Future Issuance | shares             492,217   492,217   492,217                    
Stock-based compensation expense                 $ 38,000 $ 18,000 $ 100,000 $ 100,000