DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 4,422,594	$ 3,303,570
Estimated fair value asset (liability)	4,826	1,680
Interest rate swaps
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	10,700
Total economic hedges
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	4,000,000
Total economic hedges \| Interest rate swaps
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	3,100,000
Total economic hedges \| Risk participation agreements with dealer banks
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	300,000
Total economic hedges \| Forward sale commitments
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	500,000
Designated as Hedging Instrument \| Total economic hedges
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	3,951,138	3,138,491
Estimated fair value asset (liability)	(4,179)	(2,247)
Designated as Hedging Instrument \| Total economic hedges \| Interest rate swaps \| Tax advantaged economic development bonds
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 9,744	$ 10,090
Weighted average maturity	10 years 4 months 24 days	10 years 10 months 24 days
Weighted average rate, received	2.81%	2.72%
Weighted average rate, contract pay rate	5.09%	5.09%
Estimated fair value asset (liability)	$ (1,583)	$ (1,240)
Designated as Hedging Instrument \| Total economic hedges \| Interest rate swaps \| Loans with commercial loan customers
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 1,546,563	$ 1,346,894
Weighted average maturity	6 years 8 months 12 days	6 years 8 months 12 days
Weighted average rate, received	4.47%	4.53%
Weighted average rate, contract pay rate	3.89%	4.04%
Estimated fair value asset (liability)	$ 75,114	$ 11,443
Designated as Hedging Instrument \| Total economic hedges \| Reverse interest rate swaps \| Loans with commercial loan customers
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 1,546,563	$ 1,346,894
Weighted average maturity	6 years 8 months 12 days	6 years 8 months 12 days
Weighted average rate, received	3.89%	4.04%
Weighted average rate, contract pay rate	4.47%	4.53%
Estimated fair value asset (liability)	$ (76,909)	$ (11,953)
Designated as Hedging Instrument \| Total economic hedges \| Risk participation agreements with dealer banks
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 303,793	$ 243,806
Weighted average maturity	7 years 6 months	5 years 8 months 12 days
Estimated fair value asset (liability)	$ 343	$ 237
Designated as Hedging Instrument \| Total economic hedges \| Forward sale commitments
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 544,475	$ 190,807
Weighted average maturity	6 days	6 days
Estimated fair value asset (liability)	$ (1,144)	$ (734)
Not Designated as Hedging Instrument
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	471,456	165,079
Estimated fair value asset (liability)	9,005	3,927
Not Designated as Hedging Instrument \| Commitments to lend
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional amount	$ 471,456	$ 165,079
Weighted average maturity	6 days	6 days
Estimated fair value asset (liability)	$ 9,005	$ 3,927

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- Definition

Represents information pertaining to the derivative weighted average rate which is received.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

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- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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