DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Offsetting Financial Liabilities and Derivative Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Offsetting of Financial Liabilities and Derivative Liabilities
Gross amounts not offset in the Statements of Condition, cash collateral pledged	$ 77,100
Interest rate swaps
Offsetting of Financial Liabilities and Derivative Liabilities
Gross amounts of recognized liabilities	(184,018)	$ (81,104)
Gross amounts offset in the Statements of Condition	109,253	1,219
Net amounts of liabilities presented in the Statements of Condition	(74,765)	(79,885)
Gross amounts not offset in the Statements of Condition, financial instruments	38,893	25,828
Gross amounts not offset in the Statements of Condition, cash collateral pledged	77,075	96,310
Net Amount	41,203	42,253
Interest rate swaps | Institutional counterparties
Offsetting of Financial Liabilities and Derivative Liabilities
Gross amounts of recognized liabilities	(184,018)	(80,024)
Gross amounts offset in the Statements of Condition	109,253	1,219
Net amounts of liabilities presented in the Statements of Condition	(74,765)	(78,805)
Gross amounts not offset in the Statements of Condition, financial instruments	38,893	25,828
Gross amounts not offset in the Statements of Condition, cash collateral pledged	77,075	96,310
Net Amount	41,203	43,333
Interest rate swaps | Commercial counterparties
Offsetting of Financial Liabilities and Derivative Liabilities
Gross amounts of recognized liabilities	0	(1,080)
Gross amounts offset in the Statements of Condition	0	0
Net amounts of liabilities presented in the Statements of Condition	0	(1,080)
Gross amounts not offset in the Statements of Condition, financial instruments	0	0
Gross amounts not offset in the Statements of Condition, cash collateral pledged	0	0
Net Amount	$ 0	$ (1,080)