LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 7,451,148	$ 7,314,504
Allowance for loan losses	85,997	78,008	$ 75,907
Total loans, net	$ 7,365,151	$ 7,236,496
Percent of total loans	100.00%	100.00%
Unearned loan fees in excess of unamortized costs	$ 5,800	$ (5,500)
Discount on acquired loans, net	31,100	43,700
Related party loans	4,300	7,900
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,352,999	$ 1,327,807
Percent of total loans	18.10%	18.20%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,986,336	$ 1,765,353
Percent of total loans	26.70%	24.10%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 248,150	$ 472,976
Allowance for loan losses	$ 1,360	$ 4,195	4,562
Percent of total loans	3.30%	6.50%
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 124,068	$ 72,103
Percent of total loans	1.70%	1.00%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 124,126	$ 63,846
Percent of total loans	1.70%	0.90%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 375,704	$ 278,469
Percent of total loans	5.00%	3.80%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 170,004	$ 126,773
Percent of total loans	2.30%	1.70%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 29,184	$ 33,179
Percent of total loans	0.40%	0.50%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,207,879	$ 1,207,944
Allowance for loan losses	$ 16,533	$ 13,856	12,043
Percent of total loans	16.20%	16.50%
Agricultural business, including secured by farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 369,156	$ 376,531
Allowance for loan losses	$ 2,967	$ 3,645	3,821
Percent of total loans	5.00%	5.10%
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 813,077	$ 952,633
Allowance for loan losses	$ 2,238	$ 4,732	$ 5,447
Percent of total loans	10.90%	13.00%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 493,211	$ 478,420
Percent of total loans	6.60%	6.50%
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 157,254	$ 158,470
Percent of total loans	2.10%	2.20%