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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,064,878	$ 1,192,228	$ 1,059,063	$ 1,238,876
Other comprehensive income	35,453	(18,610)	59,807	(36,374)
Ending Balance	1,022,388	1,168,856	1,022,388	1,168,856
Unrealized Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,922)		6,200
Other comprehensive income (loss) before reclassifications	(6,746)		(15,297)
Amounts reclassified from accumulated other comprehensive income	(6,351)		(16,922)
Other comprehensive income	(13,097)		(32,219)
Ending Balance	(26,019)		(26,019)
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	16,230		(27,246)
Other comprehensive income (loss) before reclassifications	48,550		92,026
Amounts reclassified from accumulated other comprehensive income	0		0
Other comprehensive income	48,550		92,026
Ending Balance	64,780		64,780
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	3,308	44,354	(21,046)	62,118
Other comprehensive income (loss) before reclassifications	41,804		76,729
Amounts reclassified from accumulated other comprehensive income	(6,351)		(16,922)
Other comprehensive income	35,453		59,807
Ending Balance	$ 38,761	$ 25,744	$ 38,761	$ 25,744