REPURCHASE AGREEMENTS AND OTHER BORROWINGS (Narrative) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Outstanding repurchase obligations	$ 3,533,786,000	$ 2,793,705,000
Fair Value of securities pledged, including accrued interest receivable	3,726,523,000	2,970,880,000
Cash Held on Deposit with Repurchase Agreement Counterparties	$ 32,349,000	$ 20,950,000
Net weighted average borrowing rate	1.54%	1.00%
Repurchase Agreement [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Outstanding repurchase obligations	$ 3,533,786,000	$ 2,793,705,000
Fair Value of securities pledged, including accrued interest receivable	3,726,523,000	2,970,880,000
Cash Held on Deposit with Repurchase Agreement Counterparties	$ 25,296,000	$ 10,835,000
Net weighted average borrowing rate	1.54%	1.00%
Aggregate amount at risk will all counterparties	$ 213,400,000