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BUSINESS COMBINATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Sep. 02, 2025	Mar. 31, 2026
Business Combination [Line Items]
Bargain purchase gain		$ 0
Mechanics Bank Acquisition
Business Combination [Line Items]
Bargain purchase gain	$ 145,460
Legacy Mechanics Bank Shareholders | Mechanics Bancorp
Business Combination [Line Items]
Economic equity interest after merger	91.70%
Voting equity interest after merger	91.30%
Legacy Homestreet, Inc. Shareholders | Mechanics Bancorp
Business Combination [Line Items]
Economic equity interest after merger	8.30%
Voting equity interest after merger	8.70%
Common Class A | Mechanics Bank Acquisition
Business Combination [Line Items]
Business combination, fixed exchange ratio	3,301.092
Common Class A | Mechanics Bank
Business Combination [Line Items]
Common stock, par value (in dollars per share)	$ 50
Common Class B | Mechanics Bank Acquisition
Business Combination [Line Items]
Business combination, fixed exchange ratio	330.1092
Common Class B | Mechanics Bank
Business Combination [Line Items]
Common stock, par value (in dollars per share)	$ 50

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