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Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Transition Adjustment of ASC 326 (Details) - USD ($) $ in Thousands			9 Months Ended
	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		$ 0	$ 10,176
Financing Receivable, Allowance for Credit Loss		155,139	384,718	$ 319,297	$ 165,575	$ 172,011	$ 196,362
Off-Balance Sheet, Credit Loss, Liability		0	6,281	7,084	0	0	412
Pre-tax effect in beginning retained eaarnings		(155,139)
Balance sheet reclassification			(229,600)
Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 8,134
Financing Receivable, Allowance for Credit Loss	236,304
Off-Balance Sheet, Credit Loss, Liability	3,922
Pre-tax effect in beginning retained eaarnings	(248,360)
Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	8,134
Financing Receivable, Allowance for Credit Loss	81,165
Off-Balance Sheet, Credit Loss, Liability	3,922
Pre-tax effect in beginning retained eaarnings	(93,221)
Balance sheet reclassification	434
Tax effect	31,333
Cumulative Effect on Retained Earnings, Net of Tax	(62,322)
Residential Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		44,806	131,781	111,450	46,032	48,284	50,794
Residential Portfolio Segment [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	94,643
Residential Portfolio Segment [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	49,837
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		15,198	42,909	38,310	17,618	21,644	32,546
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	29,929
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	14,731
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		39,194	75,726	49,435	44,848	46,373	55,581
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	19,888
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	(19,306)
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		2,370	10,241	7,800	3,059	3,026	3,592
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	3,167
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	797
Consumer Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		$ 53,571	$ 124,061	$ 112,302	$ 54,018	$ 52,684	$ 53,849
Consumer Portfolio Segment [Member] \| Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	88,677
Consumer Portfolio Segment [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 35,106