Segment Reporting (Details) $ in Thousands	3 Months Ended
Mar. 31, 2025 USD ($) segment	Mar. 31, 2024 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| segment	1
Number of operating segments \| segment	1
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 13,192	$ 9,104
Cost of product sales	0	270
Cost of manufacturing services	5,400	1,846
Research and development	39,698	46,029
Selling, general and administrative	10,718	14,709
Net loss	(41,036)	(52,190)
Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other segment income, net	1,588	1,560
Lorigerlimab \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	8,877	9,616
Vobramitanmab duocarmazine \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	8,267	9,668
MGC026 \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	5,953	3,956
MGC028 \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	3,934	6,204
MGC030 \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	2,506	1,636
Next-generation T-cell engagers \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	2,273	2,489
MGD024 \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	2,192	2,786
ADC \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	1,799	2,962
Margetuximab \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	319	3,123
Other programs \| Main Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Research and development	$ 3,578	$ 3,589

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