v3.26.3
Segment Information - Schedule of revenue and long-lived assets on the basis of geography (Details) - USD ($)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Dec. 31, 2024
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax $ 170,822,000 $ 203,457,000 $ 342,143,000 $ 401,887,000    
Operating Segments [Member]            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax $ 175,853,000 $ 209,688,000 $ 356,042,000 $ 413,468,000    
HMH Holding BV And Subsidiaries [Member]            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         $ 821,754,000 $ 843,363,000 [1]
HMH Holding BV And Subsidiaries [Member] | Operating Segments [Member]            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         848,673,000 858,967,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         249,557 233,357
HMH Holding BV And Subsidiaries [Member] | UNITED STATES            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         301,448,000 304,262,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         85,904 89,767
HMH Holding BV And Subsidiaries [Member] | NORWAY            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         203,012,000 206,155,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         38,570 25,132
HMH Holding BV And Subsidiaries [Member] | GERMANY            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         100,285,000 99,453,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         17,289 17,041
HMH Holding BV And Subsidiaries [Member] | UNITED KINGDOM            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         49,863,000 73,381,000
HMH Holding BV And Subsidiaries [Member] | SINGAPORE            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         28,278,000 45,425,000
HMH Holding BV And Subsidiaries [Member] | SAUDI ARABIA            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         27,795,000 19,314,000
HMH Holding BV And Subsidiaries [Member] | UNITED ARAB EMIRATES            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         27,584,000 19,904,000
HMH Holding BV And Subsidiaries [Member] | BRAZIL            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         25,561,000 31,827,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         28,723 25,211
HMH Holding BV And Subsidiaries [Member] | AZERBAIJAN            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         20,789,000 20,754,000
HMH Holding BV And Subsidiaries [Member] | AUSTRALIA            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         14,526,000 10,767,000
HMH Holding BV And Subsidiaries [Member] | CANADA            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         13,843,000 0
HMH Holding BV And Subsidiaries [Member] | NETHERLANDS            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         57,794 59,199
HMH Holding BV And Subsidiaries [Member] | Other [Member]            
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]            
Revenue from Contract with Customer, Including Assessed Tax         8,770,000 12,121,000
Long-Lived Asset, Excluding Financial Instrument, Customer Relationship, Mortgage Servicing Right, Deferred Policy Acquisition Cost, and Deferred Tax Asset, Amount         $ 21,277 $ 17,007
[1] As the CODM does not regularly review intersegment revenue, it is excluded from the determination of total segment operating income. The CODM uses revenue from external customers to assess performance and allocate resources.