LOANS RECEIVABLE AND THE ALLOWANCE FOR CREDIT LOSSES (Risk-Rated and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable	$ 10,163,917	$ 9,305,357	$ 8,835,368
Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	189,843
2019	191,455
2018	168,673
2017	129,494
2016	107,234
Prior	259,870
Revolving Loans	3,308
Total Loans	1,049,877
Loans receivable	1,049,877	1,580,650
Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	202,950
2019	279,942
2018	332,962
2017	271,485
2016	311,422
Prior	566,795
Revolving Loans	25,702
Total Loans	1,991,258
Loans receivable	1,991,258	2,309,221
Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	62,552
2019	68,649
2018	39,634
2017	106,938
2016	45,049
Prior	102,426
Revolving Loans	1,411
Total Loans	426,659
Loans receivable	426,659	473,152	399,814
Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	51,228
2019	110,206
2018	47,878
2017	7,549
2016	2,281
Prior	1,143
Revolving Loans	0
Total Loans	220,285
Loans receivable	220,285	210,668
Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	62,271
2019	144,695
2018	69,367
2017	14,772
2016	0
Prior	0
Revolving Loans	0
Total Loans	291,105
Loans receivable	291,105	233,610
One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	417,065
2019	88,332
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	12,688
Total Loans	518,085
Loans receivable	518,085	544,308
Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	113,282
2019	65,804
2018	25,980
2017	8,121
2016	6,773
Prior	5,706
Revolving Loans	15,137
Total Loans	240,803
Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,315,931
2019	276,012
2018	248,262
2017	88,180
2016	43,547
Prior	78,618
Revolving Loans	293,069
Total Loans	2,343,619
Loans receivable	2,343,619	1,693,824	1,619,391
Small balance CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	42,396
2019	81,877
2018	89,270
2017	79,534
2016	75,123
Prior	226,907
Revolving Loans	2,864
Total Loans	597,971
Loans receivable	597,971
Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
2020	129,749
2019	155,207
2018	139,841
2017	102,073
2016	51,552
Prior	71,627
Revolving Loans	113,775
Total Loans	763,824
Loans receivable	763,824
Consumer—home equity revolving lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,696
2019	2,083
2018	2,569
2017	3,784
2016	1,994
Prior	3,364
Revolving Loans	478,033
Total Loans	504,523
Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable	240,803	154,688
Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		26,290
Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	28,906
2019	63,947
2018	33,687
2017	25,557
2016	25,149
Prior	32,721
Revolving Loans	116,202
Total Loans	326,169
Loans receivable	326,169	370,549	390,505
One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	68,576
2019	100,443
2018	106,588
2017	125,922
2016	65,906
Prior	300,116
Revolving Loans	3,880
Total Loans	771,431
Loans receivable	771,431	945,622	$ 947,475
Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable	504,523	550,960
Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	15,173
2019	16,772
2018	16,184
2017	13,653
2016	10,055
Prior	20,811
Revolving Loans	25,660
Total Loans	118,308
Loans receivable		211,815
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		9,130,662
Pass | Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	184,182
2019	166,817
2018	165,634
2017	124,766
2016	93,179
Prior	228,160
Revolving Loans	3,159
Total Loans	965,897
Loans receivable		1,546,649
Pass | Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	190,298
2019	267,544
2018	309,233
2017	212,385
2016	281,543
Prior	523,930
Revolving Loans	21,201
Total Loans	1,806,134
Loans receivable		2,288,785
Pass | Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	62,552
2019	68,649
2018	39,634
2017	106,938
2016	45,049
Prior	102,426
Revolving Loans	1,411
Total Loans	426,659
Loans receivable		472,856
Pass | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	38,631
2019	106,658
2018	43,010
2017	6,102
2016	2,183
Prior	1,143
Revolving Loans	0
Total Loans	197,727
Loans receivable		198,986
Pass | Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	62,271
2019	144,695
2018	69,367
2017	14,772
2016	0
Prior	0
Revolving Loans	0
Total Loans	291,105
Loans receivable		233,610
Pass | One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	404,805
2019	87,377
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	12,058
Total Loans	504,240
Loans receivable		530,307
Pass | Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	113,268
2019	65,773
2018	22,930
2017	7,930
2016	6,773
Prior	5,404
Revolving Loans	15,137
Total Loans	237,215
Pass | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,304,667
2019	263,730
2018	217,169
2017	81,266
2016	42,319
Prior	78,112
Revolving Loans	256,590
Total Loans	2,243,853
Loans receivable		1,627,170
Pass | Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		764,600
Pass | Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		154,348
Pass | Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		26,256
Pass | Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	27,358
2019	60,931
2018	32,786
2017	24,415
2016	24,473
Prior	30,603
Revolving Loans	113,813
Total Loans	314,379
Loans receivable		352,408
Pass | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		940,424
Pass | Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		547,388
Pass | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		211,475
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		61,189
Special Mention | Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,369
2017	2,285
2016	0
Prior	1,616
Revolving Loans	149
Total Loans	5,419
Loans receivable		4,198
Special Mention | Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	2,153
2018	0
2017	0
2016	3,377
Prior	4,444
Revolving Loans	0
Total Loans	9,974
Loans receivable		2,193
Special Mention | Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Special Mention | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	698
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	698
Loans receivable		0
Special Mention | Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Special Mention | One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9,121
2019	623
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	630
Total Loans	10,374
Loans receivable		12,534
Special Mention | Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Special Mention | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,071
2019	502
2018	8,786
2017	834
2016	0
Prior	43
Revolving Loans	1,142
Total Loans	13,378
Loans receivable		31,012
Special Mention | Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Special Mention | Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Special Mention | Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	810
2016	0
Prior	537
Revolving Loans	0
Total Loans	1,347
Loans receivable		10,840
Special Mention | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		409
Special Mention | Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Special Mention | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		3
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		113,448
Substandard | Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,661
2019	24,638
2018	1,670
2017	2,443
2016	14,055
Prior	30,094
Revolving Loans	0
Total Loans	78,561
Loans receivable		29,803
Substandard | Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,652
2019	10,245
2018	23,729
2017	59,100
2016	26,502
Prior	38,421
Revolving Loans	4,501
Total Loans	175,150
Loans receivable		18,243
Substandard | Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		296
Substandard | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	11,899
2019	3,548
2018	4,868
2017	1,447
2016	98
Prior	0
Revolving Loans	0
Total Loans	21,860
Loans receivable		11,682
Substandard | Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Substandard | One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,139
2019	332
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	3,471
Loans receivable		1,467
Substandard | Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14
2019	31
2018	3,050
2017	191
2016	0
Prior	302
Revolving Loans	0
Total Loans	3,588
Substandard | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9,193
2019	11,780
2018	22,307
2017	6,080
2016	1,228
Prior	463
Revolving Loans	35,337
Total Loans	86,388
Loans receivable		35,584
Substandard | Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		340
Substandard | Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		34
Substandard | Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,548
2019	3,016
2018	901
2017	332
2016	676
Prior	1,581
Revolving Loans	2,389
Total Loans	10,443
Loans receivable		7,301
Substandard | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		4,789
Substandard | Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		3,572
Substandard | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		337
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		58
Doubtful | Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Doubtful | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		58
Doubtful | Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Doubtful | Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Doubtful | Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Doubtful | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Doubtful | Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Doubtful | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss | Commercial real estate - owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Commercial real estate - investment properties
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Multifamily construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | One- to four- family construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loss | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | Land and land development - residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss | Land and land development - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss | Agricultural business, including secured by farmland
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Total Loans	0
Loans receivable		0
Loss | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss | Consumer secured by one- to four-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		0
Loss | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans receivable		$ 0
Current | Small balance CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	42,396
2019	81,636
2018	89,270
2017	78,727
2016	75,123
Prior	225,523
Revolving Loans	2,864
Total Loans	595,539
Current | Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
2020	128,596
2019	154,666
2018	138,279
2017	100,654
2016	51,378
Prior	70,986
Revolving Loans	113,452
Total Loans	758,011
Current | Consumer—home equity revolving lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,696
2019	1,983
2018	2,515
2017	3,176
2016	1,665
Prior	2,945
Revolving Loans	476,385
Total Loans	501,365
Current | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	68,277
2019	100,406
2018	105,335
2017	124,930
2016	65,906
Prior	297,086
Revolving Loans	3,880
Total Loans	765,820
Current | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	15,111
2019	16,716
2018	16,158
2017	13,500
2016	10,013
Prior	20,774
Revolving Loans	25,571
Total Loans	117,843
30-59 Days Past Due | Small balance CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	241
2018	0
2017	0
2016	0
Prior	369
Revolving Loans	0
Total Loans	610
30-59 Days Past Due | Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
2020	844
2019	400
2018	207
2017	643
2016	2
Prior	240
Revolving Loans	155
Total Loans	2,491
30-59 Days Past Due | Consumer—home equity revolving lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	44
2016	0
Prior	84
Revolving Loans	745
Total Loans	873
30-59 Days Past Due | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	35
2018	0
2017	0
2016	0
Prior	195
Revolving Loans	0
Total Loans	230
30-59 Days Past Due | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18
2019	23
2018	2
2017	5
2016	37
Prior	35
Revolving Loans	63
Total Loans	183
60-89 Days Past Due | Small balance CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	622
2016	0
Prior	0
Revolving Loans	0
Total Loans	622
60-89 Days Past Due | Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
2020	224
2019	35
2018	767
2017	63
2016	0
Prior	151
Revolving Loans	58
Total Loans	1,298
60-89 Days Past Due | Consumer—home equity revolving lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	14
Revolving Loans	201
Total Loans	215
60-89 Days Past Due | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	299
2019	2
2018	241
2017	480
2016	0
Prior	727
Revolving Loans	0
Total Loans	1,749
60-89 Days Past Due | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	44
2019	33
2018	0
2017	148
2016	0
Prior	2
Revolving Loans	26
Total Loans	253
90 Days Past Due | Small balance CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	185
2016	0
Prior	1,015
Revolving Loans	0
Total Loans	1,200
90 Days Past Due | Small business scored
Financing Receivable, Credit Quality Indicator [Line Items]
2020	85
2019	106
2018	588
2017	713
2016	172
Prior	250
Revolving Loans	110
Total Loans	2,024
90 Days Past Due | Consumer—home equity revolving lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	100
2018	54
2017	564
2016	329
Prior	321
Revolving Loans	702
Total Loans	2,070
90 Days Past Due | One- to four- family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,012
2017	512
2016	0
Prior	2,108
Revolving Loans	0
Total Loans	3,632
90 Days Past Due | Consumer—other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	24
2017	0
2016	5
Prior	0
Revolving Loans	0
Total Loans	$ 29