SHARE-BASED COMPENSATION PLANS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense	$ 1,300	$ 2,600
Share-based compensation expense, tax benefit	259	733
Share-based compensation expense not yet recognized	$ 14,200
Share-based compensation expense not yet recognized, period for recognition	2 years 7 months 9 days
Mechanics Bank
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Reclassification of liability classified awards to equity	$ 13,600
Mechanics Bancorp 2025 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Equity incentive plan shares (in shares)	6,799,632
Restricted Stock Units (RSUs)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Restricted stock units vested in period, value	$ 2,300	$ 0
Restricted Stock Units (RSUs) \| Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense, vesting period	3 years
Restricted Stock Units (RSUs) \| Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense, vesting period	4 years
Performance Shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense, vesting period	3 years

Adjustments To Additional Paid in Capital, Equity Awards Reclassified From Liability To Equity

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