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, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,298,324	$ 1,390,771	$ 1,365,783
Other comprehensive income (loss) before reclassifications	(50,264)	(119,877)	(13,776)
Amounts reclassified from accumulated other comprehensive income	19,955	28,550	22,055
Other comprehensive income (loss)	(30,309)	(91,327)	8,279
Ending Balance	1,247,687	1,298,324	1,390,771
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(18,434)	(25,309)	(6,305)
Other comprehensive income (loss) before reclassifications	(1,370)	(21,675)	(41,059)
Amounts reclassified from accumulated other comprehensive income	19,955	28,550	22,055
Other comprehensive income (loss)	18,585	6,875	(19,004)
Ending Balance	151	(18,434)	(25,309)
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	154,529	252,731	225,448
Other comprehensive income (loss) before reclassifications	(48,894)	(98,202)	27,283
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive income (loss)	(48,894)	(98,202)	27,283
Ending Balance	105,635	154,529	252,731
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	136,095	227,422	219,143
Ending Balance	$ 105,786	$ 136,095	$ 227,422