LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	$ 2,016	$ 5,037
60 to 89 Days Past Due	3,222	4,256
90 Days or More Past Due	18,715	9,552
Total Past Due	23,953	18,845
Current	4,222,523	3,814,975
Total loans	4,246,476	3,833,820	$ 3,762,599
Loans 90 Days or More Past Due and Accruing	10,804	2,175
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	139	0
60 to 89 Days Past Due	0	1,984
90 Days or More Past Due	2,507	0
Total Past Due	2,646	1,984
Current	613,678	544,799
Total loans	616,324	546,783
Loans 90 Days or More Past Due and Accruing	1,835	0
Commerical real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	639
60 to 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	0	639
Current	996,714	856,303
Total loans	996,714	856,942
Loans 90 Days or More Past Due and Accruing	0	0
Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	0
90 Days or More Past Due	570	0
Total Past Due	570	0
Current	204,706	167,524
Total loans	205,276	167,524	188,792
Loans 90 Days or More Past Due and Accruing	570	0
Commercial construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	0	0
Current	45,137	17,337
Total loans	45,137	17,337
Loans 90 Days or More Past Due and Accruing	0	0
Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	0	0
Current	60,075	60,193
Total loans	60,075	60,193
Loans 90 Days or More Past Due and Accruing	0	0
One- to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	840
60 to 89 Days Past Due	0	0
90 Days or More Past Due	1,186	0
Total Past Due	1,186	840
Current	229,368	219,049
Total loans	230,554	219,889
Loans 90 Days or More Past Due and Accruing	1,186	0
Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	759
60 to 89 Days Past Due	0	0
90 Days or More Past Due	750	750
Total Past Due	750	1,509
Current	104,396	100,926
Total loans	105,146	102,435
Loans 90 Days or More Past Due and Accruing	0	0
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	0
90 Days or More Past Due	6,664	0
Total Past Due	6,664	0
Current	9,755	11,152
Total loans	16,419	11,152
Loans 90 Days or More Past Due and Accruing	4,765	0
Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	830	775
60 to 89 Days Past Due	455	35
90 Days or More Past Due	7	100
Total Past Due	1,292	910
Current	810,331	723,054
Total loans	811,623	723,964	735,128
Loans 90 Days or More Past Due and Accruing	0	0
Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	156	597
60 to 89 Days Past Due	0	466
90 Days or More Past Due	1,417	744
Total Past Due	1,573	1,807
Current	229,391	236,692
Total loans	230,964	238,499	245,742
Loans 90 Days or More Past Due and Accruing	0	0
One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	474	877
60 to 89 Days Past Due	2,607	1,623
90 Days or More Past Due	4,904	7,526
Total Past Due	7,985	10,026
Current	534,976	529,868
Total loans	542,961	539,894	$ 558,744
Loans 90 Days or More Past Due and Accruing	1,976	2,095
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	150	59
60 to 89 Days Past Due	41	60
90 Days or More Past Due	163	139
Total Past Due	354	258
Current	243,862	221,947
Total loans	244,216	222,205
Loans 90 Days or More Past Due and Accruing	0	80
Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	267	491
60 to 89 Days Past Due	119	88
90 Days or More Past Due	547	293
Total Past Due	933	872
Current	140,134	126,131
Total loans	141,067	127,003
Loans 90 Days or More Past Due and Accruing	$ 472	$ 0