REPURCHASE AGREEMENTS AND OTHER BORROWINGS - Remaining Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 3,596,721	$ 3,214,369
Repurchase agreement liabilities associated with these liabilities	$ 3,448,106	$ 3,025,052
Net weighted average borrowing rate	2.03%	2.65%
Overnight (1 Day or Less) [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 0	$ 0
Repurchase agreement liabilities associated with these liabilities	$ 0	$ 0
Net weighted average borrowing rate	0.00%	0.00%
Between 2 and 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 2,470,263	$ 1,720,804
Repurchase agreement liabilities associated with these liabilities	$ 2,361,378	$ 1,611,185
Net weighted average borrowing rate	2.04%	2.72%
Between 31 and 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 1,005,517	$ 1,493,565
Repurchase agreement liabilities associated with these liabilities	$ 964,368	$ 1,413,867
Net weighted average borrowing rate	1.94%	2.57%
Greater Than 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value of securities pledged, including accrued interest receivable	$ 120,941	$ 0
Repurchase agreement liabilities associated with these liabilities	$ 122,360	$ 0
Net weighted average borrowing rate	2.60%	0.00%