Quarterly report pursuant to Section 13 or 15(d)

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

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Clinical Trial and Sponsored Research Agreements (City of Hope - Sponsored Research and Clinical Trial Agreements) (Narrative) (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended
Sep. 08, 2021
Jul. 03, 2017
Jan. 31, 2022
Nov. 30, 2020
Oct. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Feb. 28, 2017
Mar. 31, 2022
Mar. 31, 2021
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 $ 16,289 $ 11,618
Mayo Clinic [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Total reimbursement payments made                 900  
PSCA (MB-105) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Total reimbursement payments made                 300  
HER2 (MB 103) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Total reimbursement payments made                 2,200  
CD20 (MB-106) [Member] | Fred Hutchinson Cancer Research Center [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Total reimbursement payments made                 5,200  
ST. Jude - XSCID [Member] | St. Jude Children's Research Hospital [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Total reimbursement payments made                 2,700  
Sponsored Research and Clinical Trial Agreements [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 1,592 1,842
Sponsored Research and Clinical Trial Agreements [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 0 0
Sponsored Research and Clinical Trial Agreements [Member] | Mayo Clinic [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 231 0
Sponsored Research and Clinical Trial Agreements [Member] | CD123 (MB-102) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Contribution per patient               $ 100    
Research and development expense                 51 205
Sponsored Research and Clinical Trial Agreements [Member] | CS1 (MB-104) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 50 175
Total reimbursement payments made                 1,500  
Sponsored Research and Clinical Trial Agreements [Member] | CS1 (MB-104) [Member] | City of Hope National Medical Center ("COH") [Member] | Maximum                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Milestones payable             $ 2,400      
Sponsored Research and Clinical Trial Agreements [Member] | IL13Ra2 (MB-101) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Contribution toward patient costs               $ 100    
Contribution per patient         $ 100          
Research and development expense                 228 514
Annual maintenance fee payable         200          
Sponsored Research and Clinical Trial Agreements [Member] | IL13Ra2 (MB-101) [Member] | City of Hope National Medical Center ("COH") [Member] | Maximum                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Contribution toward patient costs                 200  
Sponsored Research and Clinical Trial Agreements [Member] | PSCA (MB-105) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 22 50
Sponsored Research and Clinical Trial Agreements [Member] | PSCA (MB-105) [Member] | City of Hope National Medical Center ("COH") [Member] | Maximum                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Milestones payable         $ 2,300          
Sponsored Research and Clinical Trial Agreements [Member] | HER2 (MB 103) [Member] | City of Hope National Medical Center ("COH") [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 271 123
Sponsored Research and Clinical Trial Agreements [Member] | HER2 (MB 103) [Member] | City of Hope National Medical Center ("COH") [Member] | Maximum                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Milestones payable           $ 3,000        
Sponsored Research and Clinical Trial Agreements [Member] | CD20 (MB-106) [Member] | Fred Hutchinson Cancer Research Center [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Milestones payable   $ 5,300                
Additional milestone payments     $ 2,200 $ 1,800            
Contribution toward patient costs       $ 800            
Research and development expense                 488 671
Sponsored Research and Clinical Trial Agreements [Member] | CD20 (MB-106) [Member] | Fred Hutchinson Cancer Research Center [Member] | Maximum                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Additional milestone payments     $ 9,300              
Sponsored Research and Clinical Trial Agreements [Member] | ST. Jude - XSCID [Member] | St. Jude Children's Research Hospital [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Research and development expense                 124 104
Sponsored Research and Clinical Trial Agreements [Member] | RAG1 SCID (MB-110) [Member] | Leiden University Medical Centre [Member]                    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                    
Agreement term 5 years                  
Research and development expense                 $ 127 $ 0
Annual maintenance fee payable $ 500