LOANS RECEIVABLE AND THE ALLOWANCE FOR CREDIT LOSSES (Age Analysis of Company's Past Due Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Total loans	$ 9,146,629	$ 9,084,763
Non-accrual with no Allowance	8,580	11,765
Nonaccrual loans	17,925	22,281
Loans 90 days or more past due and still accruing	682	555
Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Total loans	872,801	831,623
Non-accrual with no Allowance	0	924
Nonaccrual loans	301	1,456
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	872,801	831,623
Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Total loans	1,670,896	1,674,027
Non-accrual with no Allowance	3,565	3,706
Nonaccrual loans	5,953	6,282
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	1,670,896	1,674,027
Small balance CRE
Financing Receivable, Past Due [Line Items]
Total loans	1,162,164	1,281,863
Non-accrual with no Allowance	3,956	5,886
Nonaccrual loans	4,364	6,421
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	1,162,164	1,281,863
Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Total loans	598,588	530,885
Non-accrual with no Allowance	0	0
Nonaccrual loans	0	0
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	598,588	530,885
Commercial construction
Financing Receivable, Past Due [Line Items]
Total loans	179,796	167,998
Non-accrual with no Allowance	0	0
Nonaccrual loans	0	98
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	179,796	167,998
Multifamily construction
Financing Receivable, Past Due [Line Items]
Total loans	274,015	259,116
Non-accrual with no Allowance	0	0
Nonaccrual loans	0	0
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	274,015	259,116
One- to four- family construction
Financing Receivable, Past Due [Line Items]
Total loans	582,800	568,753
Non-accrual with no Allowance	0	0
Nonaccrual loans	0	0
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	582,800	568,753
Land and land development - residential [Member]
Financing Receivable, Past Due [Line Items]
Total loans	317,560	313,454
Non-accrual with no Allowance	0	0
Nonaccrual loans	119	381
Loans 90 days or more past due and still accruing	0	0
Commercial Business
Financing Receivable, Past Due [Line Items]
Total loans	1,139,701	1,170,780
Non-accrual with no Allowance	38	228
Nonaccrual loans	604	1,144
Loans 90 days or more past due and still accruing	351	2
Financing Receivable, before Allowance for Credit Loss	1,139,701	1,170,780
Small business scored
Financing Receivable, Past Due [Line Items]
Total loans	817,065	792,310
Non-accrual with no Allowance	0	0
Nonaccrual loans	1,241	1,012
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	817,065	792,310
Agricultural business, including secured by farmland
Financing Receivable, Past Due [Line Items]
Total loans	245,288	280,578
Non-accrual with no Allowance	1,021	1,021
Nonaccrual loans	1,021	1,022
Loans 90 days or more past due and still accruing	0	0
Financing Receivable, before Allowance for Credit Loss	245,288	280,578
One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Total loans	718,403	657,474
Non-accrual with no Allowance	0	0
Nonaccrual loans	2,199	2,711
Loans 90 days or more past due and still accruing	210	436
Financing Receivable, before Allowance for Credit Loss	718,403	657,474
Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Total loans	470,485	458,533
Non-accrual with no Allowance	0	0
Nonaccrual loans	2,056	1,736
Loans 90 days or more past due and still accruing	114	114
Consumer-other
Financing Receivable, Past Due [Line Items]
Total loans	97,067	97,369
Non-accrual with no Allowance	0	0
Nonaccrual loans	67	18
Loans 90 days or more past due and still accruing	7	3
30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	8,647	10,527
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	0	233
30 to 59 Days Past Due [Member] | Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,504	81
30 to 59 Days Past Due [Member] | Small balance CRE
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,397	89
30 to 59 Days Past Due [Member] | Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
30 to 59 Days Past Due [Member] | Commercial construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
30 to 59 Days Past Due [Member] | Multifamily construction
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
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	162
30 to 59 Days Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	106	51
30 to 59 Days Past Due [Member] | Commercial Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	664	5,157
30 to 59 Days Past Due [Member] | Small business scored
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,078	924
30 to 59 Days Past Due [Member] | Agricultural business, including secured by farmland
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	65	139
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	1,916	2,318
30 to 59 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	668	985
30 to 59 Days Past Due [Member] | Consumer-other
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	249	388
60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	5,353	2,142
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	221	0
60 to 89 Days Past Due [Member] | Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,071	0
60 to 89 Days Past Due [Member] | Small balance CRE
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,140	0
60 to 89 Days Past Due [Member] | Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Commercial construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
60 to 89 Days Past Due [Member] | Multifamily construction
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
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 development - residential [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
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	116	1,007
60 to 89 Days Past Due [Member] | Small business scored
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	455	465
60 to 89 Days Past Due [Member] | Agricultural business, including secured by farmland
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 residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,151	327
60 to 89 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	77	268
60 to 89 Days Past Due [Member] | Consumer-other
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	122	75
90 Days or More Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	5,231	6,019
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	0	448
90 Days or More Past Due [Member] | Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
90 Days or More Past Due [Member] | Small balance CRE
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2	1,298
90 Days or More Past Due [Member] | Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
90 Days or More Past Due [Member] | Commercial construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	98
90 Days or More Past Due [Member] | Multifamily construction
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
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
90 Days or More Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	14
90 Days or More Past Due [Member] | Commercial Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	509	588
90 Days or More Past Due [Member] | Small business scored
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	864	508
90 Days or More Past Due [Member] | Agricultural business, including secured by farmland
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,021	1,021
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	1,645	1,225
90 Days or More Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,120	803
90 Days or More Past Due [Member] | Consumer-other
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	70	16
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	19,231	18,688
Financial Asset, Past Due | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	221	681
Financial Asset, Past Due | Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	3,575	81
Financial Asset, Past Due | Small balance CRE
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,539	1,387
Financial Asset, Past Due | Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
Financial Asset, Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	98
Financial Asset, Past Due | Multifamily construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	0
Financial Asset, Past Due | One- to four- family construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	162
Financial Asset, Past Due | Land and land development - residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	106	65
Financial Asset, Past Due | Commercial Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,289	6,752
Financial Asset, Past Due | Small business scored
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	3,397	1,897
Financial Asset, Past Due | Agricultural business, including secured by farmland
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,086	1,160
Financial Asset, Past Due | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	4,712	3,870
Financial Asset, Past Due | Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,865	2,056
Financial Asset, Past Due | Consumer-other
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	441	479
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	9,127,398	9,066,075
Financial Asset, Not Past Due | Commerical real estate - owner-occupied [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	872,580	830,942
Financial Asset, Not Past Due | Commercial real estate - investment properties
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,667,321	1,673,946
Financial Asset, Not Past Due | Small balance CRE
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,159,625	1,280,476
Financial Asset, Not Past Due | Multifamily Real Estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	598,588	530,885
Financial Asset, Not Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	179,796	167,900
Financial Asset, Not Past Due | Multifamily construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	274,015	259,116
Financial Asset, Not Past Due | One- to four- family construction
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	582,800	568,591
Financial Asset, Not Past Due | Land and land development - residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	317,454	313,389
Financial Asset, Not Past Due | Commercial Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,138,412	1,164,028
Financial Asset, Not Past Due | Small business scored
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	813,668	790,413
Financial Asset, Not Past Due | Agricultural business, including secured by farmland
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	244,202	279,418
Financial Asset, Not Past Due | One- to four-family residential [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	713,691	653,604
Financial Asset, Not Past Due | Consumer secured by one- to four-family [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	468,620	456,477
Financial Asset, Not Past Due | Consumer-other
Financing Receivable, Past Due [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 96,626	$ 96,890