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LOANS AND CREDIT QUALITY - Loans Held for Investment (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Loans held for investment
Total LHFI	$ 5,864,490	$ 5,542,849
Allowance for credit losses	(37,944)	(47,123)	$ (64,047)	$ (64,294)
Loans held for investment	5,826,546	5,495,726
Recurring
Loans held for investment
Single family LHFI	6,981	7,287
Recurring \| Level 3
Loans held for investment
Single family LHFI	6,981	7,287
Commercial loans
Loans held for investment
Total LHFI	4,809,480	4,476,440
Commercial loans \| Real Estate Sector
Loans held for investment
Total LHFI	3,957,186	3,616,862
Commercial loans \| Commercial and Industrial Sector
Loans held for investment
Total LHFI	852,294	859,578
Commercial loans \| Non-owner occupied CRE
Loans held for investment
Total LHFI	699,277	705,359
Commercial loans \| Multifamily
Loans held for investment
Total LHFI	2,729,775	2,415,359
Commercial loans \| Construction/land development
Loans held for investment
Total LHFI	528,134	496,144
Commercial loans \| Owner occupied CRE
Loans held for investment
Total LHFI	464,356	457,706
Commercial loans \| Commercial business
Loans held for investment
Total LHFI	387,938	401,872
Consumer loans
Loans held for investment
Total LHFI	1,055,010	1,066,409
Consumer loans \| Single family
Loans held for investment
Total LHFI	759,286	763,331
Consumer loans \| Home equity and other
Loans held for investment
Total LHFI	$ 295,724	$ 303,078