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No definition available.

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- Definition

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+ References

No definition available.

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Collaboration Agreements - Other Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Collaboration agreements
Collaboration revenue	$ 844	$ 2,151	$ 42,081	$ 9,405
Type of Revenue	mrsn:CollaborationMember	mrsn:CollaborationMember	mrsn:CollaborationMember	mrsn:CollaborationMember
Accounts receivable	$ 298		$ 298		$ 459
Asana BioSciences
Collaboration agreements
Next potential milestone payment eligible to receive	2,500		2,500
Asana BioSciences \| Limited services
Collaboration agreements
Collaboration revenue	10	$ 587	25	$ 782
Asana BioSciences \| Milestone
Collaboration agreements
Collaboration revenue	$ 0		$ 0	$ 1,500