USE OF DERIVATIVES, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME BY COMPONENT - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,238,876	$ 1,247,687	$ 1,298,324
Other comprehensive income (loss)	(83,164)	(43,773)	(30,309)
Ending Balance	1,059,063	1,238,876	1,247,687
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	16,874	151	(18,434)
Other comprehensive (loss) before reclassifications	25,716	21,426	(1,370)
Amounts reclassified from accumulated other comprehensive income	(36,390)	(4,808)	19,955
Cumulative effect adjustment		105
Other comprehensive income (loss)	(10,674)	16,723	18,585
Ending Balance	6,200	16,874	151
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	45,244	105,635	154,529
Other comprehensive (loss) before reclassifications	(72,490)	(60,391)	(48,894)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Cumulative effect adjustment		0
Other comprehensive income (loss)	(72,490)	(60,391)	(48,894)
Ending Balance	(27,246)	45,244	105,635
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	62,118	105,786	136,095
Other comprehensive (loss) before reclassifications	(46,774)	(38,965)	(50,264)
Amounts reclassified from accumulated other comprehensive income	(36,390)	(4,808)	19,955
Cumulative effect adjustment		105
Other comprehensive income (loss)	(83,164)	(43,668)	(30,309)
Ending Balance	$ (21,046)	$ 62,118	$ 105,786