LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 7,185,999	$ 7,314,504		$ 4,105,399
Allowance for loan losses	78,197	78,008	$ 78,008	75,365	$ 75,907
Net loans	$ 7,107,802	$ 7,236,496
Percent of total loans	100.00%	100.00%
Unearned loan fees in excess of unamortized costs	$ 2,800	$ (5,500)
Discount on acquired loans, net	42,300	43,700
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 1,328,034	$ 1,327,807
Percent of total loans	18.50%	18.20%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 1,805,243	$ 1,765,353
Percent of total loans	25.10%	24.10%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 307,019	$ 472,976		208,687
Allowance for loan losses	$ 2,853		4,195	4,401	4,562
Percent of total loans	4.30%	6.50%
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 87,711	$ 72,103
Percent of total loans	1.20%	1.00%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 79,737	$ 63,846
Percent of total loans	1.10%	0.90%
One- to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 297,348	$ 278,469
Percent of total loans	4.10%	3.80%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 142,841	$ 126,773
Percent of total loans	2.00%	1.70%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 24,493	$ 33,179
Percent of total loans	0.30%	0.50%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 1,224,915	$ 1,207,944		776,579
Allowance for loan losses	$ 15,118		13,856	12,892	12,043
Percent of total loans	17.10%	16.50%
Agricultural business, including secured by farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 340,350	$ 376,531		208,635
Allowance for loan losses	$ 4,282		3,645	3,732	2,821
Percent of total loans	4.70%	5.10%
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 910,719	$ 952,633		543,004
Allowance for loan losses	$ 2,170		$ 4,732	$ 8,141	$ 8,447
Percent of total loans	12.70%	13.00%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 481,590	$ 478,420
Percent of total loans	6.70%	6.50%
Consumer - other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 155,999	$ 158,470
Percent of total loans	2.20%	2.20%