LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	$ 5,037,000		$ 6,366,000
60 to 89 Days Past Due	4,256,000		4,086,000
90 Days or More Past Due	9,552,000		11,558,000
Total Past Due	18,845,000		22,010,000
Current	3,814,975,000		3,396,435,000
Total loans outstanding	3,833,820,000		3,418,445,000
Loans 90 Days or More Past Due and Accruing	2,175,000		2,860,000
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	0		883,000
60 to 89 Days Past Due	1,984,000		550,000
90 Days or More Past Due	0		813,000
Total Past Due	1,984,000		2,246,000
Current	544,799,000		500,355,000
Total loans outstanding	546,783,000		502,601,000
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	639,000		0
60 to 89 Days Past Due	0		0
90 Days or More Past Due	0		0
Total Past Due	639,000		0
Current	856,303,000		692,457,000
Total loans outstanding	856,942,000		692,457,000
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		1,845,000
60 to 89 Days Past Due	0		785,000
90 Days or More Past Due	0		0
Total Past Due	0		2,630,000
Current	167,524,000		134,523,000
Total loans outstanding	167,524,000		137,153,000
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	17,337,000		12,168,000
Total loans outstanding	17,337,000		12,168,000
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	60,193,000		52,081,000
Total loans outstanding	60,193,000		52,081,000
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	840,000		9,000
60 to 89 Days Past Due	0		7,000
90 Days or More Past Due	0		4,000
Total Past Due	840,000		20,000
Current	219,049,000		200,844,000
Total loans outstanding	219,889,000		200,864,000
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	759,000		0
60 to 89 Days Past Due	0		0
90 Days or More Past Due	750,000		251,000
Total Past Due	1,509,000		251,000
Current	100,926,000		75,444,000
Total loans outstanding	102,435,000		75,695,000
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	0		0
Total Past Due	0		0
Current	11,152,000		10,450,000
Total loans outstanding	11,152,000		10,450,000
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	775,000		2,001,000
60 to 89 Days Past Due	35,000		2,000
90 Days or More Past Due	100,000		299,000
Total Past Due	910,000		2,302,000
Current	723,054,000		679,867,000
Total loans outstanding	723,964,000		682,169,000
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	597,000		0
60 to 89 Days Past Due	466,000		0
90 Days or More Past Due	744,000		0
Total Past Due	1,807,000		0
Current	236,692,000		228,291,000
Total loans outstanding	238,499,000		228,291,000
Loans 90 Days or More Past Due and Accruing	0		105,000
One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	877,000	[1]	521,000	[1]
60 to 89 Days Past Due	1,623,000		2,550,000
90 Days or More Past Due	7,526,000		9,142,000
Total Past Due	10,026,000		12,213,000
Current	529,868,000		517,281,000
Total loans outstanding	539,894,000		529,494,000
Loans 90 Days or More Past Due and Accruing	2,095,000		2,611,000
Exactly 30 Days Past Due, Not Included in Past Due Loans	8,000,000	[1]	6,000,000	[1]
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	59,000		723,000
60 to 89 Days Past Due	60,000		93,000
90 Days or More Past Due	139,000		918,000
Total Past Due	258,000		1,734,000
Current	221,947,000		171,454,000
Total loans outstanding	222,205,000		173,188,000
Loans 90 Days or More Past Due and Accruing	80,000		13,000
Consumer - other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	491,000		384,000
60 to 89 Days Past Due	88,000		99,000
90 Days or More Past Due	293,000		131,000
Total Past Due	872,000		614,000
Current	126,131,000		121,220,000
Total loans outstanding	127,003,000		121,834,000
Loans 90 Days or More Past Due and Accruing	$ 0		$ 131,000

[1] (1) One- to four-family loans are not considered past due until they exceed 30 days and are not reflected herein. One- to four-family loans exactly 30 days past due at December 31, 2014 and 2013 were $8 million and $6 million, respectively.