USE OF DERIVATIVE FINANCIAL INSTRUMENTS, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME BY COMPONENT - Changes in AOCI (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated other comprehensive income (loss) [Line Items]
Beginning Balance	$ 219,143	$ 293,910	$ 204,540
Other comprehensive income (loss) before reclassifications	(13,776)	(91,681)	69,488
Amounts reclassified from accumulated other comprehensive income	22,055	16,914	19,882
Other comprehensive income (loss)	8,279	(74,767)	89,370
Ending Balance	227,422	219,143	293,910
Gains and Losses on Cash Flow Hedges [Member]
Accumulated other comprehensive income (loss) [Line Items]
Beginning Balance	(6,305)	(32,539)	(30,159)
Other comprehensive income (loss) before reclassifications	(41,059)	9,320	(22,262)
Amounts reclassified from accumulated other comprehensive income	22,055	16,914	19,882
Other comprehensive income (loss)	(19,004)	26,234	(2,380)
Ending Balance	(25,309)	(6,305)	(32,539)
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated other comprehensive income (loss) [Line Items]
Beginning Balance	225,448	326,449	234,699
Other comprehensive income (loss) before reclassifications	27,283	(101,001)	91,750
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive income (loss)	27,283	(101,001)	91,750
Ending Balance	$ 252,731	$ 225,448	$ 326,449