LOANS AND CREDIT QUALITY - Aging Analysis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 5,864,490	$ 5,542,849
Nonaccrual	11,846	12,201
Total past due and nonaccrual	$ 24,415	$ 21,020
Nonaccrual, percent of total loans	0.20%	0.22%
Past due and nonaccrual, percent of total loans	0.42%	0.38%
Percent of total loans	100.00%	100.00%
Federal Housing Administration, Veteran Affairs, Or Small Business Administration
Financing Receivable, Past Due [Line Items]
Total past due and nonaccrual	$ 11,000	$ 8,400
Recurring
Financing Receivable, Past Due [Line Items]
Single family LHFI	6,981	7,287
Level 3 | Recurring
Financing Receivable, Past Due [Line Items]
Single family LHFI	6,981	7,287
30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 3,814	$ 1,208
Past due, percent of total loans	0.07%	0.02%
60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 1,852	$ 894
Past due, percent of total loans	0.03%	0.02%
90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 6,903	$ 6,717
Past due, percent of total loans	0.12%	0.12%
Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 5,840,075	$ 5,521,829
Not past due, percent of total loans	99.58%	99.62%
Commercial loans, adjusted for credit analysis | Real Estate Sector
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 3,957,186	$ 3,616,862
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Real Estate Sector | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Real Estate Sector | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Real Estate Sector | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Real Estate Sector | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	3,957,186	3,616,862
Commercial loans, adjusted for credit analysis | Commercial and Industrial Sector
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	852,294	859,578
Nonaccrual	7,535	8,591
Total past due and nonaccrual	7,535	8,789
Commercial loans, adjusted for credit analysis | Commercial and Industrial Sector | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	198
Commercial loans, adjusted for credit analysis | Commercial and Industrial Sector | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Commercial and Industrial Sector | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Commercial and Industrial Sector | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	844,759	850,789
Commercial loans, adjusted for credit analysis | Non-owner occupied CRE
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	699,277	705,359
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Non-owner occupied CRE | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Non-owner occupied CRE | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Non-owner occupied CRE | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Non-owner occupied CRE | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	699,277	705,359
Commercial loans, adjusted for credit analysis | Multifamily
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	2,729,775	2,415,359
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Multifamily | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	2,729,775	2,415,359
Commercial loans, adjusted for credit analysis | Multifamily construction
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	36,827	37,861
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Multifamily construction | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily construction | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily construction | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Multifamily construction | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	36,827	37,861
Commercial loans, adjusted for credit analysis | CRE construction
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	18,099	14,172
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | CRE construction | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | CRE construction | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | CRE construction | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | CRE construction | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	18,099	14,172
Commercial loans, adjusted for credit analysis | Single family construction
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	318,800	296,027
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Single family construction | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	318,800	296,027
Commercial loans, adjusted for credit analysis | Single family construction to permanent
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	154,408	148,084
Nonaccrual	0	0
Total past due and nonaccrual	0	0
Commercial loans, adjusted for credit analysis | Single family construction to permanent | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction to permanent | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction to permanent | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Single family construction to permanent | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	154,408	148,084
Commercial loans, adjusted for credit analysis | Owner occupied CRE
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	464,356	457,706
Nonaccrual	3,539	3,568
Total past due and nonaccrual	3,539	3,568
Commercial loans, adjusted for credit analysis | Owner occupied CRE | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Owner occupied CRE | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Owner occupied CRE | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Owner occupied CRE | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	460,817	454,138
Commercial loans, adjusted for credit analysis | Commercial business
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	387,938	401,872
Nonaccrual	3,996	5,023
Total past due and nonaccrual	3,996	5,221
Commercial loans, adjusted for credit analysis | Commercial business | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	198
Commercial loans, adjusted for credit analysis | Commercial business | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Commercial business | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Commercial loans, adjusted for credit analysis | Commercial business | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	383,942	396,651
Consumer portfolio segment, adjusted for credit analysis
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	1,055,010	1,066,409
Nonaccrual	4,311	3,610
Total past due and nonaccrual	16,880	12,231
Consumer portfolio segment, adjusted for credit analysis | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	3,814	1,010
Consumer portfolio segment, adjusted for credit analysis | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	1,852	894
Consumer portfolio segment, adjusted for credit analysis | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	6,903	6,717
Consumer portfolio segment, adjusted for credit analysis | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	1,038,130	1,054,178
Consumer portfolio segment, adjusted for credit analysis | Single family
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	759,286	763,331
Nonaccrual	2,918	2,802
Total past due and nonaccrual	15,395	11,231
Consumer portfolio segment, adjusted for credit analysis | Single family | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	3,753	892
Consumer portfolio segment, adjusted for credit analysis | Single family | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	1,821	820
Consumer portfolio segment, adjusted for credit analysis | Single family | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	6,903	6,717
Consumer portfolio segment, adjusted for credit analysis | Single family | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	743,891	752,100
Consumer portfolio segment, adjusted for credit analysis | Home equity and other
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	295,724	303,078
Nonaccrual	1,393	808
Total past due and nonaccrual	1,485	1,000
Consumer portfolio segment, adjusted for credit analysis | Home equity and other | 30-59 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	61	118
Consumer portfolio segment, adjusted for credit analysis | Home equity and other | 60-89 days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	31	74
Consumer portfolio segment, adjusted for credit analysis | Home equity and other | 90+ days
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	0	0
Consumer portfolio segment, adjusted for credit analysis | Home equity and other | Current
Financing Receivable, Past Due [Line Items]
Loans before allowance for credit loss	$ 294,239	$ 302,078