LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 36,083	$ 24,733
Purchased Credit-Impaired	38,674	58,600	$ 5,409
Current	7,323,880	7,231,171
Total loans	7,398,637	7,314,504	4,372,594
Loans 90 days or more past due and still accruing	1,424	952
Nonaccrual loans	25,872	14,270
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,810	5,005
Purchased Credit-Impaired	14,921	24,261
Current	1,321,846	1,298,541
Total loans	1,340,577	1,327,807
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	1,360	1,235
Commerical real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	11,645	4,398
Purchased Credit-Impaired	13,623	16,724
Current	1,893,371	1,744,231
Total loans	1,918,639	1,765,353
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	11,416	2,516
Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	246	4
Purchased Credit-Impaired	258	1,994	441
Current	266,379	470,978
Total loans	266,883	472,976	198,874
Loans 90 days or more past due and still accruing	147	0
Nonaccrual loans	30	0
Commercial construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Purchased Credit-Impaired	0	0
Current	135,487	72,103
Total loans	135,487	72,103
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	0	0
Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	784
Purchased Credit-Impaired	0	0
Current	105,669	63,062
Total loans	105,669	63,846
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	0	0
One- to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	752	2,686
Purchased Credit-Impaired	881	905
Current	361,953	274,878
Total loans	363,586	278,469
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	0	1,233
Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	750	747
Purchased Credit-Impaired	0	77
Current	161,279	125,949
Total loans	162,029	126,773
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	750	1,027
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	997	96
Purchased Credit-Impaired	3,272	4,668
Current	26,287	28,415
Total loans	30,556	33,179
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	997	0
Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,383	3,042
Purchased Credit-Impaired	4,264	7,302	0
Current	1,180,201	1,197,600
Total loans	1,187,848	1,207,944	812,070
Loans 90 days or more past due and still accruing	0	8
Nonaccrual loans	2,765	2,159
Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7,071	1,330
Purchased Credit-Impaired	807	1,529	0
Current	375,397	373,672
Total loans	383,275	376,531	242,556
Loans 90 days or more past due and still accruing	0	0
Nonaccrual loans	3,755	697
One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,819	5,304
Purchased Credit-Impaired	301	1,066	0
Current	842,779	946,263
Total loans	846,899	952,633	$ 536,325
Loans 90 days or more past due and still accruing	852	899
Nonaccrual loans	3,414	4,700
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,552	563
Purchased Credit-Impaired	80	40
Current	495,011	477,817
Total loans	497,643	478,420
Loans 90 days or more past due and still accruing	253	4
Nonaccrual loans	1,150	565
Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,058	774
Purchased Credit-Impaired	267	34
Current	158,221	157,662
Total loans	159,546	158,470
Loans 90 days or more past due and still accruing	172	41
Nonaccrual loans	235	138
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7,986	12,725
30 to 59 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	638	3,981
30 to 59 Days Past Due [Member] | Commerical real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	504	1,763
30 to 59 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	99	4
30 to 59 Days Past Due [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30 to 59 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	771
30 to 59 Days Past Due [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	300	2,466
30 to 59 Days Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30 to 59 Days Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30 to 59 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	419	1,844
30 to 59 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,864	323
30 to 59 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	488	620
30 to 59 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,158	465
30 to 59 Days Past Due [Member] | Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	516	488
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5,140	2,591
60 to 89 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,681	139
60 to 89 Days Past Due [Member] | Commerical real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	229	132
60 to 89 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	13
60 to 89 Days Past Due [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	452	220
60 to 89 Days Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	96
60 to 89 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	333	174
60 to 89 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	729
60 to 89 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	648	873
60 to 89 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	578	60
60 to 89 Days Past Due [Member] | Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	219	155
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	22,957	9,417
90 Days or More Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	491	885
90 Days or More Past Due [Member] | Commerical real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	10,912	2,503
90 Days or More Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	147	0
90 Days or More Past Due [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	750	747
90 Days or More Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	997	0
90 Days or More Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,631	1,024
90 Days or More Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,207	278
90 Days or More Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,683	3,811
90 Days or More Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	816	38
90 Days or More Past Due [Member] | Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 323	$ 131