LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	$ 6,607	$ 5,037
60 to 89 Days Past Due	3,179	4,256
90 Days or More Past Due	11,396	9,552
Total Past Due	21,182	18,845
Current	4,093,636	3,814,975
Total loans outstanding	4,114,818	3,833,820	3,522,912
Loans 90 Days or More Past Due and Accruing	1,555	2,175
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	2,254	0
60 to 89 Days Past Due	1,589	1,984
90 Days or More Past Due	815	0
Total Past Due	4,658	1,984
Current	622,873	544,799
Total loans outstanding	627,531	546,783
Loans 90 Days or More Past Due and Accruing	0	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	910	0
Total Past Due	910	639
Current	935,783	856,303
Total loans outstanding	936,693	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	578	0
Total Past Due	578	0
Current	208,109	167,524
Total loans outstanding	208,687	167,524	153,003
Loans 90 Days or More Past Due and Accruing	0	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	30,434	17,337
Total loans outstanding	30,434	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	56,201	60,193
Total loans outstanding	56,201	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	1,494	840
60 to 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	1,494	840
Current	226,730	219,049
Total loans outstanding	228,224	219,889
Loans 90 Days or More Past Due and Accruing	0	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	98,180	100,926
Total loans outstanding	98,930	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	1,225	0
Total Past Due	1,225	0
Current	15,949	11,152
Total loans outstanding	17,174	11,152
Loans 90 Days or More Past Due and Accruing	0	0
Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	350	775
60 to 89 Days Past Due	63	35
90 Days or More Past Due	0	100
Total Past Due	413	910
Current	776,166	723,054
Total loans outstanding	776,579	723,964	716,546
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	803	597
60 to 89 Days Past Due	395	466
90 Days or More Past Due	1,021	744
Total Past Due	2,219	1,807
Current	206,416	236,692
Total loans outstanding	208,635	238,499	208,817
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	897	877
60 to 89 Days Past Due	943	1,623
90 Days or More Past Due	5,279	7,526
Total Past Due	7,119	10,026
Current	545,304	529,868
Total loans outstanding	552,423	539,894	517,621
Loans 90 Days or More Past Due and Accruing	1,548	2,095
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	431	59
60 to 89 Days Past Due	103	60
90 Days or More Past Due	121	139
Total Past Due	655	258
Current	232,988	221,947
Total loans outstanding	233,643	222,205
Loans 90 Days or More Past Due and Accruing	6	80
Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	378	491
60 to 89 Days Past Due	86	88
90 Days or More Past Due	697	293
Total Past Due	1,161	872
Current	138,503	126,131
Total loans outstanding	139,664	127,003
Loans 90 Days or More Past Due and Accruing	$ 1	$ 0