v3.26.3
Segment Information - Reconciliation of Reportable Segment Revenues (Details) - USD ($)
$ in Thousands
 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 [Line Items]            
Total revenue $ 170,822 $ 203,457 $ 342,143 $ 401,887    
HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         $ 821,754 $ 843,363 [1]
Intersegment Eliminations            
Segment Reporting [Line Items]            
Total revenue (5,031) (6,231) (13,899) (11,581)    
Intersegment Eliminations | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         (26,919) (15,604)
Operating Segments            
Segment Reporting [Line Items]            
Total revenue 175,853 209,688 356,042 413,468    
Operating Segments | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         848,673 858,967
ESS            
Segment Reporting [Line Items]            
Total revenue 97,660 125,547 198,350 233,088    
ESS | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue [1]         438,553 443,189
ESS | Intersegment Eliminations            
Segment Reporting [Line Items]            
Total revenue (2,766) (2,690) (8,015) (4,808)    
ESS | Intersegment Eliminations | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         (15,252) (5,489)
ESS | Operating Segments            
Segment Reporting [Line Items]            
Total revenue 100,426 128,237 206,365 237,896    
ESS | Operating Segments | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         453,805 448,678
PCS            
Segment Reporting [Line Items]            
Total revenue 73,162 77,910 143,793 168,799    
PCS | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue [1]         383,201 400,174
PCS | Intersegment Eliminations            
Segment Reporting [Line Items]            
Total revenue (2,265) (3,541) (5,884) (6,773)    
PCS | Intersegment Eliminations | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         (11,667) (10,115)
PCS | Operating Segments            
Segment Reporting [Line Items]            
Total revenue $ 75,427 $ 81,451 $ 149,677 $ 175,572    
PCS | Operating Segments | HMH Holding BV And Subsidiaries [Member]            
Segment Reporting [Line Items]            
Total revenue         $ 394,868 $ 410,289
[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.