Stock-Based Compensation - Schedule of Total Stock-based Compensation Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock compensation expense	$ 11,288	$ 10,748	$ 30,961	$ 25,985
Location, Statement of Income, Balance [Axis]: us-gaap:GeneralAndAdministrativeExpense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock compensation expense	5,133	1,610	13,300	4,051
Location, Statement of Income, Balance [Axis]: us-gaap:ResearchAndDevelopmentExpense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock compensation expense	1,177	2,470	3,759	5,870
Location, Statement of Income, Balance [Axis]: us-gaap:SellingAndMarketingExpense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock compensation expense	2,413	3,059	6,264	7,282
Location, Statement of Income, Balance [Axis]: xmtr:OperationsAndSupportExpense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock compensation expense	$ 2,565	$ 3,609	$ 7,638	$ 8,782