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Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Commission revenue by fee type |  |  |
Revenues | $ 846,268 | $ 817,097 | $ 752,547
Commissions [Member] |  |  |
Commission revenue by fee type |  |  |
Disclosed trading | 376,599 | 361,252 | 323,038
Open Trading - matched principal trading | 175,557 | 177,966 | 178,517
Other Variable Transaction | 30,263 | 20,016 | 4,979
Total variable transaction fees | 600,448 | 578,544 | 521,756
Distribution fees and unused minimum fees | 134,175 | 133,166 | 141,208
Revenues | 734,623 | 711,710 | 662,964
Commissions [Member] | US Government Bonds [Member] |  |  |
Commission revenue by fee type |  |  |
Open Trading - matched principal trading | $ 18,029 | $ 19,310 | $ 15,222

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