USE OF DERIVATIVES, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,059,063	$ 1,238,876
Other comprehensive income	24,354	(17,764)
Ending Balance	1,064,878	1,192,228
Unrealized Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	6,200
Other comprehensive income (loss) before reclassifications	(8,551)
Amounts reclassified from Accumulated other comprehensive income (loss)	(10,571)
Other comprehensive income	(19,122)
Ending Balance	(12,922)
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(27,246)
Other comprehensive income (loss) before reclassifications	43,476
Amounts reclassified from Accumulated other comprehensive income (loss)	0
Other comprehensive income	43,476
Ending Balance	16,230
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(21,046)	62,118
Other comprehensive income (loss) before reclassifications	34,835
Amounts reclassified from Accumulated other comprehensive income (loss)	(10,481)
Other comprehensive income	24,354
Ending Balance	$ 3,308	$ 44,354