FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	$ 38,808	$ 29,188
Financial assets
Investment securities held-to-maturity	158,305	429,328
Other investments	115,731	115,660
Deposits
Noninterest-bearing	2,488,157	2,492,434
Savings	3,100,894	3,167,325
Time	2,309,810	2,173,564
Carrying value
Financial assets
Cash and short-term investments	219,228	273,959
Investment securities held-to-maturity	158,305	429,328
Other investments	115,731	115,660
Loans held for sale	8,217	4,372
Loans and leases	8,752,479	8,767,672
Interest Receivable	44,171	41,816
Deposits
Deposits	10,133,897	10,140,394
Short-term borrowings	1,047,415	1,040,691
Long-term debt	546,423	570,739
Interest Payable	12,449	12,126
Fair value
Financial assets
Cash and short-term investments	219,228	273,959
Investment securities held-to-maturity	153,075	424,118
Loans held for sale	8,217	4,372
Loans and leases	8,651,343	8,662,868
Interest Receivable	44,171	41,816
Deposits
Deposits	10,117,317	10,113,475
Short-term borrowings	1,047,415	1,040,691
Long-term debt	538,743	557,933
Interest Payable	12,449	12,126
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	219,228	273,959
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans and leases	0	0
Interest Receivable	0	0
Deposits
Deposits	0	0
Short-term borrowings	1,047,415	1,040,691
Long-term debt	0	0
Interest Payable	2,907	2,035
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	153,075	424,118
Loans held for sale	8,217	4,372
Loans and leases	0	0
Interest Receivable	14,230	13,819
Deposits
Deposits	10,117,317	10,113,475
Short-term borrowings	0	0
Long-term debt	538,743	557,933
Interest Payable	9,542	10,091
Fair Value, Inputs, Level 3 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans and leases	8,651,343	8,662,868
Interest Receivable	29,941	27,997
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0