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Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Commission revenue by fee type |  |  |  |
Revenues | $ 208,821 | $ 206,715 | $ 636,859 | $ 614,693
Commissions [Member] |  |  |  |
Commission revenue by fee type |  |  |  |
Disclosed trading | 92,640 | 91,273 | 286,183 | 272,828
Open Trading - matched principal trading | 40,590 | 45,137 | 130,961 | 135,756
Other Variable Transaction | 8,590 | 4,802 | 20,882 | 14,728
Total variable transaction fees | 145,949 | 146,737 | 452,013 | 436,696
Distribution fees and unused minimum fees | 34,222 | 33,655 | 101,271 | 100,248
Revenues | 180,171 | 180,392 | 553,284 | 536,944
Commissions [Member] | US Government Bonds [Member] |  |  |  |
Commission revenue by fee type |  |  |  |
Open Trading - matched principal trading | $ 4,129 | $ 5,525 | $ 13,987 | $ 13,384

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