USE OF DERIVATIVES, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME BY COMPONENT - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,238,876
Other comprehensive income (loss)	(17,764)	$ 13,753
Ending Balance	1,192,228
Unrealized Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	16,874
Other comprehensive income (loss) before reclassifications	30,933
Amounts reclassified from accumulated other comprehensive income	(4,644)
Other comprehensive income (loss)	26,289
Ending Balance	43,163
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	45,244
Other comprehensive income (loss) before reclassifications	(44,053)
Amounts reclassified from accumulated other comprehensive income	0
Other comprehensive income (loss)	(44,053)
Ending Balance	1,191
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	62,118
Other comprehensive income (loss) before reclassifications	(13,120)
Amounts reclassified from accumulated other comprehensive income	(4,644)
Other comprehensive income (loss)	(17,764)
Ending Balance	$ 44,354