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No definition available.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Collaboration agreements - 2016 Takeda and XMT-1522 Agreements - Accounting (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounting analysis
Research and development		$ 11,412	$ 7,555	$ 32,145	$ 23,163
2016 Restated Tokeda Agreement and XMT-1522 Agreement
Accounting analysis
Total arrangement consideration	$ 50,089	46,148		46,148
Upfront payment received	13,500
Expected fees for research services	9,515	4,160		4,160
Remaining deferred revenue	7,498
Non-creditable portion of XMT-1522 upfront fee	13,250
Expected reimbursement for related services	6,326	7,740		7,740
License consideration and research plan extension fee received				800
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, First designated target
Accounting analysis
Selling price allocation	4,502
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Research license and related services, Second designated target
Accounting analysis
Selling price allocation	1,362
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Discount on exclusive license, Second designated target
Accounting analysis
Selling price allocation	553
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, Third designated target
Accounting analysis
Selling price allocation	4,546
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, Fourth designated target
Accounting analysis
Selling price allocation	4,975
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, Fifth designated target
Accounting analysis
Selling price allocation	4,975
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, Sixth designated target
Accounting analysis
Selling price allocation	4,975
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Exclusive development and commercialization license and related research services, Seventh designated target
Accounting analysis
Selling price allocation	4,975
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| First replacement right, Designated target
Accounting analysis
Selling price allocation	3,685
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Discount on second replacement right, Designated target
Accounting analysis
Selling price allocation	3,276
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Future technological improvements
Accounting analysis
Selling price allocation	1,843
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Joint research committee services, Takeda
Accounting analysis
Selling price allocation	157
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| License and related services, XMT-1522
Accounting analysis
Selling price allocation	39,901
2016 Restated Tokeda Agreement and XMT-1522 Agreement \| Joint research committee services, XMT-1522
Accounting analysis
Selling price allocation	472
XMT-1522 Agreement
Accounting analysis
Research and development		$ 924	$ 196	$ 1,719	$ 353
Upfront payment received	$ 26,500