Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Impact Of Derivative Instruments On Statements Of Financial Performance And Financial Position) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Related net interest payable	$ (7,788,000)	[1]	$ (10,023,000)	[1]
Interest rate swap agreements at fair value, net assets (liability)	(40,487,000)		(40,754,000)
Derivative instruments unrealized losses to be recognized	15,300,000
Amount of gain (loss) reclassified from AOCI related to the effective portion	(19,882,000)		(28,066,000)		(27,546,000)
Amount of loss recognized (ineffective portion)	(542,000)		(827,000)		(140,000)
Increase in interest expense and decrease in Net income as a result of the use of Derivatives	(20,424,000)	[2]	(28,893,000)	[2]	(27,686,000)	[2]
Amount of loss recognized in other comprehensive income (effective portion)	(22,262,000)		(51,751,000)		(27,587,000)
Repurchase Arrangements And Similar Borrowings [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Repurchase arrangements and similar borrowings	169,000	[3]	617,000	[3]
Repurchase arrangements and similar borrowings	(18,671,000)	[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	(14,197,000)	[3]	(15,657,000)	[3]
Effective Portion Of Active Positions [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Amount of gain (loss) reclassified from AOCI related to the effective portion	(19,882,000)		(28,066,000)		(27,554,000)
Effective Portion Of Terminated Positions [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Amount of gain (loss) reclassified from AOCI related to the effective portion					$ 8,000

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

[2] (a) 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 primarily in the form of fixed-rate swap payments in excess of current market rates totaled $15.3 million at December 31, 2012.