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, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	$ 6,363	$ 9,870
60 to 89 Days Past Due	2,323	4,264
Greater Than 90 Days Past Due	17,713	19,267
Total Past Due	26,399	33,401
Current	3,213,922	3,202,313
Total loans outstanding	3,240,321	3,235,714	3,229,662
Loans 90 Days or More Past Due and Accruing	2,289	3,029
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,794	1,693
60 to 89 Days Past Due	4	0
Greater Than 90 Days Past Due	824	1,371
Total Past Due	2,622	3,064
Current	494,820	486,517
Total loans outstanding	497,442	489,581	468,318
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	715	743
60 to 89 Days Past Due	49	0
Greater Than 90 Days Past Due	1,410	1,431
Total Past Due	2,174	2,174
Current	600,587	581,467
Total loans outstanding	602,761	583,641	612,617
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
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	134,290	137,504
Total loans outstanding	134,290	137,504	132,306
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
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	34,762	30,229
Total loans outstanding	34,762	30,229	40,276
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
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	34,147	22,581
Total loans outstanding	34,147	22,581	20,654
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	430	611
60 to 89 Days Past Due	0	0
Greater Than 90 Days Past Due	196	0
Total Past Due	626	611
Current	171,250	160,204
Total loans outstanding	171,876	160,815	148,717
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	286	0
60 to 89 Days Past Due	0	0
Greater Than 90 Days Past Due	1,777	2,047
Total Past Due	2,063	2,047
Current	76,383	74,963
Total loans outstanding	78,446	77,010	89,329
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	2,083
60 to 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	45
Total Past Due	0	2,128
Current	12,477	11,854
Total loans outstanding	12,477	13,982	12,044
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	1,326	1,849
60 to 89 Days Past Due	248	49
Greater Than 90 Days Past Due	1,430	842
Total Past Due	3,004	2,740
Current	616,474	615,309
Total loans outstanding	619,478	618,049	609,497
Loans 90 Days or More Past Due and Accruing	0	0
Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	181	0
60 to 89 Days Past Due	30	0
Greater Than 90 Days Past Due	0	0
Total Past Due	211	0
Current	210,014	230,031
Total loans outstanding	210,225	230,031	188,955
Loans 90 Days or More Past Due and Accruing	0	0
One- to four-family real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	241	1,376
60 to 89 Days Past Due	1,802	3,468
Greater Than 90 Days Past Due	9,422	11,488
Total Past Due	11,465	16,332
Current	555,265	565,338
Total loans outstanding	566,730	581,670	619,511
Loans 90 Days or More Past Due and Accruing	2,243	2,877
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	1,261	816
60 to 89 Days Past Due	190	673
Greater Than 90 Days Past Due	1,062	839
Total Past Due	2,513	2,328
Current	109,869	118,170
Total loans outstanding	112,382	120,498	106,978
Loans 90 Days or More Past Due and Accruing	46	152
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 to 59 Days Past Due	129	699
60 to 89 Days Past Due	0	74
Greater Than 90 Days Past Due	1,592	1,204
Total Past Due	1,721	1,977
Current	163,584	168,146
Total loans outstanding	165,305	170,123	180,460
Loans 90 Days or More Past Due and Accruing	$ 0	$ 0