REPURCHASE AGREEMENTS AND OTHER BORROWINGS (Narrative) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Outstanding repurchase obligations	$ 3,449,854,000	$ 3,533,786,000
Fair Value of securities pledged, including accrued interest receivable	3,658,329,000	3,726,523,000
Cash Held on Deposit with Repurchase Agreement Counterparties	$ 31,065,000	$ 32,349,000
Net weighted average borrowing rate	2.07%	1.54%
Repurchase Agreement [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Outstanding repurchase obligations	$ 3,449,854,000	$ 3,533,786,000
Fair Value of securities pledged, including accrued interest receivable	3,658,329,000	3,726,523,000
Cash Held on Deposit with Repurchase Agreement Counterparties	$ 23,093,000	$ 25,296,000
Net weighted average borrowing rate	2.07%	1.54%
Aggregate amount at risk will all counterparties	$ 224,300,000