FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets
Investment securities held-to-maturity	$ 118,072	$ 142,862
Other investments	118,292	125,020
Interest Receivable	41,225
Deposits
Noninterest-bearing	3,552,893	2,643,928
Savings	3,446,678	2,960,979
Time	1,935,392	2,240,441
Carrying value
Financial assets
Cash and short-term investments	245,934	257,639
Investment securities held-to-maturity	118,072	142,862
Other investments	118,292	125,020
Loans held for sale	69,008	13,680
Loans and leases	10,032,265	9,144,015
Interest Receivable	53,127	39,591
Deposits
Deposits	11,567,430	10,210,229
Short-term borrowings	247,658	1,316,181
Long-term debt	1,341,164	414,376
Interest Payable	9,112	13,671
Fair value
Financial assets
Cash and short-term investments	245,934	257,639
Investment securities held-to-maturity	123,441	142,821
Loans held for sale	69,008	13,680
Loans and leases	9,953,876	9,134,215
Interest Receivable	53,127	39,591
Deposits
Deposits	11,576,499	10,209,790
Short-term borrowings	247,658	1,316,181
Long-term debt	1,337,424	414,937
Interest Payable	9,112	13,671
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	245,934	257,639
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	247,658	1,316,181
Long-term debt	0	0
Interest Payable	104	1,899
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	123,441	142,821
Loans held for sale	69,008	13,680
Loans and leases	0	0
Interest Receivable	11,902	12,743
Deposits
Deposits	11,576,499	10,209,790
Short-term borrowings	0	0
Long-term debt	1,337,424	414,937
Interest Payable	9,008	11,772
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	9,953,876	9,134,215
Interest Receivable		26,848
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0