Clinical Trial and Sponsored Research Agreements (Sponsored Research and Clinical Trial Agreements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ 15,164	$ 10,902	$ 31,453	$ 22,520
Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	1,456	1,260	3,048	3,102
City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	0	0	0	0
Mayo Clinic [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	231	233	462	233
CD123 (MB-102) [Member] | City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	52	21	103	226
IL13Ra2 (MB-101) [Member] | City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	234	279	462	793
CS1 (MB-104) [Member] | City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	50	197	100	372
HER2 (MB 103) [Member] | City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	271	31	542	154
PSCA (MB-105) [Member] | City of Hope National Medical Center ("COH") [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	28		50	46
Research and Development (Income) Expenses		(4)
CD20 (MB-106) [Member] | Fred Hutchinson Cancer Research Center [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	358	327	846	998
ST. Jude - XSCID [Member] | St. Jude Children's Research Hospital [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	94	176	218	280
RAG1 SCID (MB-110) [Member] | Leiden University Medical Centre [Member] | Sponsored Research and Clinical Trial Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ 138	$ 0	$ 265	$ 0