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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) shares in Thousands | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2021 shares | Dec. 31, 2024 USD ($) reporting_unit tranche revenueSource shares | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Concentration Risk [Line Items] |  |  |  |
Number of sources of revenue | revenueSource |  | 4 |  |
Number of days to take exam |  | 21 days |  |
Advertising costs |  | $ 62,373,000 | $ 52,969,000 | $ 48,111,000
Compensation expense |  | $ 110,477,000 | 95,221,000 | 73,820,000
Number of reporting units | reporting_unit |  | 1 |  |
Impairment |  | $ 0 | 0 | 0
Impairment of capitalized software |  | $ 238,000 | 0 | 0
Impairment, Long-Lived Asset, Held-for-Use, Statement of Income or Comprehensive Income [Extensible Enumeration] |  | Impairment of capitalized software |  |
RSUs outstanding |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Vesting period (in years) |  | 4 years |  |
Equity instruments other than options, grants in period (in shares) | shares |  | 719 |  |
Founder awards where performance has been met |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Compensation expense |  | $ 19,799,000 | $ 26,622,000 | $ 30,997,000
Founder awards where performance has been met | Founders |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Equity instruments other than options, grants in period (in shares) | shares | 1,800 |  |  |
Number of tranches | tranche |  | 10 |  |
Apple | Accounts Receivable | Customer Concentration Risk |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration risk (in percent) |  | 64.70% | 65.20% |
Google | Accounts Receivable | Customer Concentration Risk |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration risk (in percent) |  | 21.20% | 20.70% |
Stripe | Accounts Receivable | Customer Concentration Risk |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration risk (in percent) |  |  | 10.70% |
Capitalized Software |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Estimated useful life (in years) |  | 3 years |  |

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