ACQUISITION - Acquired Performing Loans (Details) - Diboll State Bancshares, Inc. - Performing loans $ in Thousands	Nov. 30, 2017 USD ($)
Business Acquisition [Line Items]
Fair Value at Acquisition Date	$ 581,981
Contractual Amounts Receivable	823,974
Cash Flows Not Expected to be Collected at Acquisition Date	127,399	[1]
Construction Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	40,122
Contractual Amounts Receivable	56,905
Cash Flows Not Expected to be Collected at Acquisition Date	330	[1]
1-4 Family Residential Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	82,654
Contractual Amounts Receivable	130,167
Cash Flows Not Expected to be Collected at Acquisition Date	26,894	[1]
Commercial Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	319,623
Contractual Amounts Receivable	484,529
Cash Flows Not Expected to be Collected at Acquisition Date	97,431	[1]
Commercial Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	82,083
Contractual Amounts Receivable	87,688
Cash Flows Not Expected to be Collected at Acquisition Date	1,226	[1]
Municipal Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	7,848
Contractual Amounts Receivable	9,998
Cash Flows Not Expected to be Collected at Acquisition Date	28
Loans to Individuals
Business Acquisition [Line Items]
Fair Value at Acquisition Date	49,651
Contractual Amounts Receivable	54,687
Cash Flows Not Expected to be Collected at Acquisition Date	$ 1,490	[1]

[1] Cash flows not expected to be collected relate to estimated credit losses and expected prepayments.