STOCK-BASED COMPENSATION - Stock Settled Appreciation Rights (Details) - SSARs - USD ($) $ in Millions		9 Months Ended
Mar. 01, 2025	Sep. 30, 2025
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Fair value of SSARs that have vested		$ 3.6
CrossFirst \| Common \| CrossFirst
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares received for each share owned (in shares)	0.6675
Omnibus Incentive 2018 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period		7 years
Weighted average remaining contractual term		5 years 4 months 24 days
Period over which cost will be recognized		3 years 2 months 12 days
Omnibus Incentive 2018 Plan \| Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation, expiration period		10 years
Omnibus Incentive 2018 Plan \| Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation, expiration period		15 years

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