Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Impact Of Derivative Instruments On Statements Of Financial Performance And Financial Position) (Detail) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Related net interest payable	$ (7,462,000)	[1]			$ (7,462,000)	[1]			$ (10,023,000)	[1]
Interest rate swap agreements at fair value, net assets (liability)	(45,336,000)				(45,336,000)				(40,754,000)
Derivative instruments unrealized losses to be recognized					16,000,000
Amount of gain (loss) recognized (ineffective portion)	(448,000)		109,000		(307,000)		(49,000)
Increase in interest expense and decrease in Net income as a result of the use of derivatives	(5,278,000)	[2]	(7,358,000)	[2]	(10,102,000)	[2]	(13,628,000)	[2]
Amount of loss recognized in other comprehensive income (loss) (effective portion)	(15,334,000)		(16,883,000)		(17,085,000)		(17,561,000)
Repurchase Arrangements And Similar Borrowings [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Repurchase arrangements and similar borrowings, an asset									617,000	[3]
Repurchase arrangements and similar borrowings, a liability	(19,175,000)	[3]			(19,175,000)	[3]			(15,691,000)	[3]
Unsecured Borrowings [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Repurchase arrangements and similar borrowings, a liability	(18,699,000)	[3]			(18,699,000)	[3]			(15,657,000)	[3]
Effective Portion Of Active Positions [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Effective portion of active positions	$ (4,830,000)		$ (7,467,000)		$ (9,795,000)		$ (13,579,000)

[1] Included in "Accounts payable and accrued expenses" on the face of the balance sheet.

[2] Included in "Interest expense: Repurchase arrangements and similar borrowings" on the face of the statement of income.

[3] The fair value of derivatives with realized and unrealized gains are aggregated and recorded as an asset on the face of the balance sheet separately from the fair value of derivatives with realized and unrealized losses that are recorded as a liability. The amount of unrealized losses that will be recognized in the statement of income over the next twelve months in the form of fixed- and variable-rate swap payments in excess of current market rates totaled $16.0 million at June 30, 2012.