FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets
Investment securities held-to-maturity	$ 148,778	$ 429,328
Other investments	124,965	115,660
Deposits
Noninterest-bearing	2,534,739	2,492,434
Savings	2,924,200	3,167,325
Time	2,308,617	2,173,564
Carrying value
Financial assets
Cash and short-term investments	282,151	273,959
Investment securities held-to-maturity	148,778	429,328
Other investments	124,965	115,660
Loans held for sale	23,528	4,372
Loans and leases	9,007,126	8,767,672
Interest Receivable	41,321	41,816
Deposits
Deposits	10,083,857	10,140,394
Short-term borrowings	1,214,186	1,040,691
Long-term debt	498,778	570,739
Interest Payable	13,287	12,126
Fair value
Financial assets
Cash and short-term investments	282,151	273,959
Investment securities held-to-maturity	149,724	424,118
Loans held for sale	23,528	4,372
Loans and leases	8,918,940	8,662,868
Interest Receivable	41,321	41,816
Deposits
Deposits	10,083,186	10,113,475
Short-term borrowings	1,214,186	1,040,691
Long-term debt	501,174	557,933
Interest Payable	13,287	12,126
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	282,151	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	1,214,186	1,040,691
Long-term debt	0	0
Interest Payable	3,179	2,035
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	149,724	424,118
Loans held for sale	23,528	4,372
Loans and leases	0	0
Interest Receivable	12,653	13,819
Deposits
Deposits	10,083,186	10,113,475
Short-term borrowings	0	0
Long-term debt	501,174	557,933
Interest Payable	10,108	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	8,918,940	8,662,868
Interest Receivable	28,668	27,997
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0