FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	$ 27,565	$ 12,687
Financial assets
Investment securities held-to-maturity	443,957	654,008
Other investments	95,004	53,140
Deposits
Noninterest-bearing	2,471,932	1,662,058
Savings	3,087,683	2,462,420
Time	2,104,044	1,317,105
Carrying value
Financial assets
Cash and short-term investments	254,582	184,624
Investment securities held-to-maturity	443,957	654,008
Other investments	95,004	53,140
Loans held for sale	15,821	11,502
Loans and leases	8,830,505	5,959,162
Interest Receivable	40,152	24,496
Deposits
Deposits	10,103,747	6,895,046
Short-term borrowings	1,188,303	814,565
Long-term debt	469,423	119,654
Interest Payable	9,550	5,104
Fair value
Financial assets
Cash and short-term investments	254,582	184,624
Investment securities held-to-maturity	435,785	653,101
Loans held for sale	15,821	11,502
Loans and leases	8,847,519	6,006,656
Interest Receivable	40,152	24,496
Deposits
Deposits	10,073,140	6,884,615
Short-term borrowings	1,188,303	814,565
Long-term debt	462,478	117,908
Interest Payable	9,550	5,104
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	254,582	184,624
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	1,188,303	814,565
Long-term debt	0	0
Interest Payable	1,577	204
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	435,785	653,101
Loans held for sale	15,821	11,502
Loans and leases	0	0
Interest Receivable	13,939	8,265
Deposits
Deposits	10,073,140	6,884,615
Short-term borrowings	0	0
Long-term debt	462,478	117,908
Interest Payable	7,973	4,900
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	8,847,519	6,006,656
Interest Receivable	26,213	16,231
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0