USE OF DERIVATIVE FINANCIAL INSTRUMENTS, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME BY COMPONENT - Balance Sheet and Income Statement Location (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Balance sheet-related [Abstract]
Interest rate swap agreements at fair value, net assets (liability)	$ (34,893)		$ (11,792)
Income statement-related [Abstract]
Amount of loss reclassified from Accumulated other comprehensive income related to the effective portion of active positions	22,055		16,914		19,882
Other Comprehensive Income (Loss) [Member]
Other comprehensive income related [Abstract]
Amount of gain (loss) recognized in Other comprehensive income (loss) (effective portion)	(41,059)		9,320		(22,262)
Interest Expense [Member]
Income statement-related [Abstract]
Amount of loss reclassified from Accumulated other comprehensive income related to the effective portion of active positions	(22,055)		(16,914)		(19,882)
Amount of gain (loss) recognized (ineffective portion)	(473)		24		(542)
Increase in interest expense and decrease in Net income as a result of the use of Derivatives	(22,528)	[1]	(16,890)	[1]	(20,424)	[1]
Other Assets [Member]
Balance sheet-related [Abstract]
Related net interest payable	(9,516)	[2]	(5,493)	[2]
Borrowings Under Repurchase Arrangements [Member] | Other Assets [Member]
Balance sheet-related [Abstract]
Interest rate swap agreements in a gain position (an asset)	1,657	[3]	1,094	[3]
Interest rate swap agreements in a loss position (a liability)	(6,332)	[3]	(11,304)	[3]
Unsecured Borrowings [Member] | Other Assets [Member]
Balance sheet-related [Abstract]
Interest rate swap agreements in a gain position (an asset)	0	[3]	3,911	[3]
Interest rate swap agreements in a loss position (a liability)	$ (20,702)	[3]	$ 0	[3]

[1] Included in Interest expense: Repurchase arrangements and similar borrowings on the face of the Statements of Income.

[2] Included in "Accounts payable and accrued expenses" on the face of the Balance Sheets.

[3] The fair value of Derivatives with realized and unrealized gains are aggregated and recorded as an asset on the face of the Balance Sheets separately from the fair value of Derivatives with realized and unrealized losses that are recorded as a liability. The amount of unrealized losses scheduled to be recognized in the Statements of Income over the next twelve months primarily in the form of fixed-rate swap payments in excess of current market rates totaled $12.2 million at December 31, 2014.