Net Interest Income Analysis (Summary Of Interest Income, Interest Expense And Weighted Average Interest Rates) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Dec. 31, 2011
Component of Other Expense, Nonoperating [Line Items]
Residential mortgage investments	$ 63,463		$ 62,890	$ 194,983		$ 179,167
Other	154		59	480		230
Interest Income	63,617		62,949	195,463		179,397
Repurchase arrangements and similar borrowings	(17,875)		(15,744)	(48,429)		(41,772)
Unsecured borrowings	(2,186)		(2,186)	(6,560)		(6,560)
Other						(5)
Interest expense	(20,061)		(17,930)	(54,989)		(48,337)
Net interest income (expense)	43,556		45,019	140,474		131,060
Residential mortgage investments	1.86%		2.17%	2.01%		2.29%
Other	0.15%		0.09%	0.16%		0.13%
Income Income	1.81%		2.12%	1.95%		2.25%
Repurchase arrangements and similar borrowings	0.56%		0.57%	0.53%		0.57%
Unsecured borrowings	8.49%	[1]	8.49%	8.49%	[1]	8.49%	0.37%
Other			0.08%	0.07%		0.14%
Interest expense	0.62%		0.65%	0.60%		0.65%
Net interest income (expense)	1.19%		1.47%	1.35%		1.60%
Related Changes In Rate [Member]
Component of Other Expense, Nonoperating [Line Items]
Residential mortgage investments	(9,707)	[2]		(23,646)	[2]
Other	54	[2]		63	[2]
Interest Income	(9,653)	[2]		(23,583)	[2]
Repurchase arrangements and similar borrowings	(274)	[2]		(3,055)	[2]
Unsecured borrowings		[2]			[2]
Other				(2)	[2]
Interest expense	(274)	[2]		(3,057)	[2]
Net interest income (expense)	(9,379)	[2]		(20,526)	[2]
Related Changes In Volume [Member]
Component of Other Expense, Nonoperating [Line Items]
Residential mortgage investments	10,280	[2]		39,462	[2]
Other	41	[2]		187	[2]
Interest Income	10,321	[2]		39,649	[2]
Repurchase arrangements and similar borrowings	2,405	[2]		9,712	[2]
Unsecured borrowings		[2]			[2]
Other				(3)	[2]
Interest expense	2,405	[2]		9,709	[2]
Net interest income (expense)	7,916	[2]		29,940	[2]
Related Changes In Total [Member]
Component of Other Expense, Nonoperating [Line Items]
Residential mortgage investments	573	[2]		15,816	[2]
Other	95	[2]		250	[2]
Interest Income	668	[2]		16,066	[2]
Repurchase arrangements and similar borrowings	2,131	[2]		6,657	[2]
Unsecured borrowings		[2]			[2]
Other				(5)	[2]
Interest expense	2,131	[2]		6,652	[2]
Net interest income (expense)	$ (1,463)	[2]		$ 9,414	[2]

[1] After considering cash flow hedges that coincide with the floating rate terms of these borrowings that begin in 2015 and 2016, the effective borrowing rate during the final 20 years of these borrowings will average 7.56%, subject to certain adjustments for the effects of measured hedge ineffectiveness, if any.

[2] The change in interest income and interest expense due to both volume and rate has been allocated to volume and rate changes in proportion to the relationship of the absolute dollar amounts of the change in each.