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Collaboration Agreements - Narrative (Detail) |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 60 Months Ended |  |
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Jan. 02, 2019 | Jun. 30, 2014 USD ($) target milestone | Mar. 31, 2019 USD ($) | Dec. 31, 2021 USD ($) target | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) agreement | Dec. 31, 2019 USD ($) agreement | Jan. 01, 2018 USD ($) | Jan. 31, 2016 target
Collaboration agreements |  |  |  |  |  |  |  |  |
Deferred revenue |  |  |  | $ 3,944,000 | $ 3,987,000 | $ 4,815,000 | $ 4,815,000 |  |
Amounts included in the contract liability at the beginning of the period |  |  |  | 43,000 | 828,000 |  |  |  |
Collaboration revenue |  |  |  | 43,000 | 828,000 | 42,123,000 |  |  |
Research and development |  |  |  | 132,013,000 | 67,036,000 | 55,040,000 |  |  |
Merck KGaA |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Upfront payment received |  | $ 12,000,000 |  |  |  |  |  |  |
Number of targets | target |  | 6 |  |  |  |  |  |  |
Amount of additional fees receivable when target is designated and commercial license to target is granted |  | $ 0 |  |  |  |  |  |  |
Aggregate milestones |  | 780,000,000 |  |  |  |  |  |  |
Development milestones |  | 84,000,000 |  |  |  |  |  |  |
Regulatory milestones |  | 264,000,000 |  |  |  |  |  |  |
Sales milestones |  | $ 432,000,000 |  |  |  |  |  |  |
Number of individual development milestones per target | milestone |  | 6 |  |  |  |  |  |  |
Number of individual regulatory milestones per target | milestone |  | 5 |  |  |  |  |  |  |
Number of individual commercial milestones | milestone |  | 3 |  |  |  |  |  |  |
Amount of development milestone payment received |  |  |  | 0 | 0 |  | $ 3,000,000 |  |
Next potential development milestone payment eligible to receive |  |  |  | $ 500,000 |  |  |  |  |
Prior written notice for termination period |  |  |  | 60 days |  |  |  |  |
Number of targets designated | target |  |  |  | 6 |  |  |  |  |
Revenue, transaction price, amount |  |  |  | $ 21,325,000 | 21,325,000 |  |  |  |
Number of service obligations completed of designated targets | target |  |  |  | 4 |  |  |  |  |
Collaboration revenue |  |  |  | $ 43,000 | 828,000 | 853,000 |  |  |
Milestone Payment Not Received, Included in Estimated Transaction Price |  |  |  |  |  |  |  | $ 0 |
Merck KGaA | License and corresponding research and development services, first and second targets |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | 3,941,000 |  |  |  |  |
Merck KGaA | License and corresponding research and development services, third and sixth target |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | 3,439,000 |  |  |  |  |
Merck KGaA | License and corresponding research and development services, fourth target |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | 3,152,000 |  |  |  |  |
Merck KGaA | License and corresponding research and development services, fifth target |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | 2,746,000 |  |  |  |  |
Merck KGaA | Rights to future technological improvements |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | $ 425,000 |  |  |  |  |
Merck KGaA | Rights to future technological improvements | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Expected recognition period |  |  |  | 10 years |  |  |  |  |
Merck KGaA | Joint research committee services |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Revenue, transaction price, amount |  |  |  | $ 242,000 |  |  |  |  |
Merck KGaA | Joint research committee services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Expected recognition period |  |  |  | 5 years |  |  |  |  |
Merck KGaA Agreement and Merck KGaA supply agreement |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Accounts receivable |  |  |  | $ 0 | 0 |  |  |  |
Deferred revenue |  |  |  | 3,944,000 | 3,987,000 |  |  |  |
XMT-1522 agreement |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Period of time until agreement terminated | 30 days |  |  |  |  |  |  |  |
Period of shared development costs following effective termination date | 30 days |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  | 200,000 |  |  |
ASC 808 costs billed to Takeda |  |  |  |  |  | $ 195,000 |  |  |
2016 Restated Tokeda agreement |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Number of targets | target |  |  |  |  |  |  |  |  | 7
Period of time until agreement terminated | 45 days |  |  |  |  |  |  |  |
2016 Restated Tokeda agreement and XMT-1522 agreement |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Amounts included in the contract liability at the beginning of the period |  |  | $ 39,965,000 |  |  |  |  |  |
Number of performance obligations | agreement |  |  |  |  |  | 14 | 14 |  |
Collaboration revenue |  |  |  | 0 | 0 | $ 39,965,000 |  |  |
2016 Restated Tokeda agreement and XMT-1522 agreement | License and related research and development services, including phase 1 development and transfer certain materials and know how |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Number of performance obligations | agreement |  |  |  |  |  | 1 | 1 |  |
Asana BioSciences |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Next potential milestone payment eligible to receive |  |  |  | 2,500,000 |  |  |  |  |
Asana BioSciences | Limited services |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Collaboration revenue |  |  |  | 0 | 0 | $ 25,000 |  |  |
Merck KGaA supply agreement |  |  |  |  |  |  |  |  |
Collaboration agreements |  |  |  |  |  |  |  |  |
Collaboration revenue |  |  |  | $ 0 | $ 0 | $ 1,280,000 |  |  |

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