SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impact of Adoption (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities held to maturity, allowance for credit losses	$ 60
Allowance for credit loss	343,000	$ 196,000	$ 196,000	$ 186,000	$ 180,000
Allowance for credit losses on off-balance sheet credit exposures		3,000
As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		301,000
Allowance for credit losses on off-balance sheet credit exposures		13,000
Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		105,000
Allowance for credit losses on off-balance sheet credit exposures		10,000
States of the U.S. and Political Subdivisions (municipals) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities held to maturity, allowance for credit losses	60	0
States of the U.S. and Political Subdivisions (municipals) [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities held to maturity, allowance for credit losses		0
States of the U.S. and Political Subdivisions (municipals) [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities held to maturity, allowance for credit losses		0
Commercial Real Estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	152,000	60,000	60,000
Commercial Real Estate [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		138,000
Commercial Real Estate [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		78,000
Commercial and Industrial [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	88,000	53,000	53,000
Commercial and Industrial [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		65,000
Commercial and Industrial [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		12,000
Commercial Leases [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	13,000	11,000	11,000
Commercial Leases [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		11,000
Commercial Leases [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		0
Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	1,000	9,000	9,000
Other [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		0
Other [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		(9,000)
Direct Installment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	26,000	13,000	13,000
Direct Installment [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		24,000
Direct Installment [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		11,000
Residential Mortgages [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	31,000	22,000	22,000
Residential Mortgages [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		32,000
Residential Mortgages [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		10,000
Indirect Installment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	21,000	19,000	19,000
Indirect Installment [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		21,000
Indirect Installment [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		2,000
Consumer Lines of Credit [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	$ 11,000	9,000	$ 9,000
Consumer Lines of Credit [Member] | As Reported Under ASC 326 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		10,000
Consumer Lines of Credit [Member] | Impact of ASC 326 Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		$ 1,000