LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans and Leases Receivable, Gross	$ 9,084,763	$ 9,870,982
Financing Receivable, Nonaccrual, No Allowance	11,765	19,586
Financing Receivable, Nonaccrual	22,281	32,560
Loans 90 Days or More Past Due and Accruing	555	3,054
Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,131,828	1,076,467
Loans and Leases Receivable, Gross	1,131,828	1,076,467
Financing Receivable, Nonaccrual, No Allowance	3,809	7,509
Financing Receivable, Nonaccrual	4,340	8,429
Loans 90 Days or More Past Due and Accruing	0	0
Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,990,461	1,955,684
Loans and Leases Receivable, Gross	1,990,461	1,955,684
Financing Receivable, Nonaccrual, No Allowance	4,892	8,979
Financing Receivable, Nonaccrual	7,468	8,979
Loans 90 Days or More Past Due and Accruing	0	0
Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	598,212	573,849
Loans and Leases Receivable, Gross	598,212	573,849
Financing Receivable, Nonaccrual, No Allowance	1,815	567
Financing Receivable, Nonaccrual	2,351	791
Loans 90 Days or More Past Due and Accruing	0	0
Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	564,100	428,223
Loans and Leases Receivable, Gross	564,100	428,223
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	0	0
Loans 90 Days or More Past Due and Accruing	0	0
Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	169,530	228,937
Loans and Leases Receivable, Gross	169,530	228,937
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	98	98
Loans 90 Days or More Past Due and Accruing	0	0
Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	259,116	305,527
Loans and Leases Receivable, Gross	259,116	305,527
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	0	0
Loans 90 Days or More Past Due and Accruing	0	0
One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	568,753	507,810
Loans and Leases Receivable, Gross	568,753	507,810
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	0	331
Loans 90 Days or More Past Due and Accruing	0	0
Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	313,454	248,915
Loans and Leases Receivable, Gross	313,454	248,915
Financing Receivable, Nonaccrual, No Allowance	0	302
Financing Receivable, Nonaccrual	381	507
Loans 90 Days or More Past Due and Accruing	0	0
Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,172,076	2,178,461
Loans and Leases Receivable, Gross	1,172,076	2,178,461
Financing Receivable, Nonaccrual, No Allowance	228	555
Financing Receivable, Nonaccrual	1,144	1,988
Loans 90 Days or More Past Due and Accruing	2	889
Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	792,310	743,451
Loans and Leases Receivable, Gross	792,310	743,451
Financing Receivable, Nonaccrual, No Allowance	0	91
Financing Receivable, Nonaccrual	1,012	3,419
Loans 90 Days or More Past Due and Accruing	0	136
Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	285,753	299,949
Loans and Leases Receivable, Gross	285,753	299,949
Financing Receivable, Nonaccrual, No Allowance	1,021	1,412
Financing Receivable, Nonaccrual	1,022	1,743
Loans 90 Days or More Past Due and Accruing	0	0
One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	683,268	717,939
Loans and Leases Receivable, Gross	683,268	717,939
Financing Receivable, Nonaccrual, No Allowance	0	171
Financing Receivable, Nonaccrual	2,711	3,556
Loans 90 Days or More Past Due and Accruing	436	1,899
Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	458,533	491,812
Loans and Leases Receivable, Gross	458,533	491,812
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	1,736	2,697
Loans 90 Days or More Past Due and Accruing	114	130
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	97,369	113,958
Loans and Leases Receivable, Gross	97,369	113,958
Financing Receivable, Nonaccrual, No Allowance	0	0
Financing Receivable, Nonaccrual	18	22
Loans 90 Days or More Past Due and Accruing	3	0
30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	10,527	10,675
30 to 59 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	233	0
30 to 59 Days Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	81	0
30 to 59 Days Past Due [Member] | Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	89	0
30 to 59 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
30 to 59 Days Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
30 to 59 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
30 to 59 Days Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	162	356
30 to 59 Days Past Due [Member] | Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	51	0
30 to 59 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	5,157	3,247
30 to 59 Days Past Due [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	924	1,459
30 to 59 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	139	298
30 to 59 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,318	4,620
30 to 59 Days Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	985	459
30 to 59 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	388	236
60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,142	2,908
60 to 89 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	182
60 to 89 Days Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	45
60 to 89 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,007	31
60 to 89 Days Past Due [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	465	891
60 to 89 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	37
60 to 89 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	327	955
60 to 89 Days Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	268	439
60 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	75	328
90 Days or More Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	6,019	22,548
90 Days or More Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	448	1,447
90 Days or More Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,186	7,981
90 Days or More Past Due [Member] | Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	112	790
90 Days or More Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
90 Days or More Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	98	98
90 Days or More Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
90 Days or More Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	331
90 Days or More Past Due [Member] | Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	14	317
90 Days or More Past Due [Member] | Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	588	2,088
90 Days or More Past Due [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	508	2,048
90 Days or More Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,021	1,548
90 Days or More Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,225	4,053
90 Days or More Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	803	1,847
90 Days or More Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	16	0
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	18,688	36,131
Financial Asset, Past Due | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	681	1,629
Financial Asset, Past Due | Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,267	7,981
Financial Asset, Past Due | Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	201	835
Financial Asset, Past Due | Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
Financial Asset, Past Due | Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	98	98
Financial Asset, Past Due | Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
Financial Asset, Past Due | One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	162	687
Financial Asset, Past Due | Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	65	317
Financial Asset, Past Due | Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	6,752	5,366
Financial Asset, Past Due | Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,897	4,398
Financial Asset, Past Due | Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,160	1,883
Financial Asset, Past Due | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	3,870	9,628
Financial Asset, Past Due | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,056	2,745
Financial Asset, Past Due | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	479	564
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	9,066,075	9,834,851
Financial Asset, Not Past Due | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,131,147	1,074,838
Financial Asset, Not Past Due | Commercial real estate - investment properties [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,989,194	1,947,703
Financial Asset, Not Past Due | Small Balance CRE [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	598,011	573,014
Financial Asset, Not Past Due | Multifamily real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	564,100	428,223
Financial Asset, Not Past Due | Commercial Construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	169,432	228,839
Financial Asset, Not Past Due | Multifamily construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	259,116	305,527
Financial Asset, Not Past Due | One-to four-family construction [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	568,591	507,123
Financial Asset, Not Past Due | Land and Land Improvements [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	313,389	248,598
Financial Asset, Not Past Due | Commercial business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,165,324	2,173,095
Financial Asset, Not Past Due | Small Credit-Scored Business Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	790,413	739,053
Financial Asset, Not Past Due | Agricultural business, including secured by farmland [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	284,593	298,066
Financial Asset, Not Past Due | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	679,398	708,311
Financial Asset, Not Past Due | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	456,477	489,067
Financial Asset, Not Past Due | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 96,890	$ 113,394