Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Schedule Of Repurchase Arrangements And Similar Borrowings) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Collateral Carrying Amount	$ 13,450,000		$ 11,930,000
Borrowings Outstanding	12,784,238		11,352,444
Average Borrowing Rates	8.49%	[1]	8.49%	8.49%
Agency Securities [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Collateral Carrying Amount	13,453,159		11,929,514
Accrued Interest Receivable	32,858		27,181
Borrowings Outstanding	12,784,238		11,352,444
Average Borrowing Rates	0.47%		0.37%
Year-End Borrowing Rates Adjusted For Effects Of Related Derivatives Held As Cash Flow Hedges [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Average Borrowing Rates	0.65%		0.58%
Borrowings With Maturities Of 30 Days Or Less [Member] | Agency Securities [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Collateral Carrying Amount	13,406,253		11,306,478
Accrued Interest Receivable	32,807		25,630
Borrowings Outstanding	12,739,872		10,754,835
Average Borrowing Rates	0.47%		0.37%
Borrowings With Maturities Of 31 To 90 Days [Member] | Agency Securities [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Collateral Carrying Amount	44,060		619,710
Accrued Interest Receivable	51		1,551
Borrowings Outstanding	41,520		594,283
Average Borrowing Rates	0.57%		0.32%
Collateral For Structured Financings [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Collateral Carrying Amount	2,846		3,326
Borrowings Outstanding	$ 2,846		$ 3,326
Average Borrowing Rates	8.12%		8.04%

[1] After considering cash flow hedges that coincide with the floating rate terms of these borrowings that begin in October and December 2015 for the Capstead Mortgage Trust I and II notes and September 2016 for the Capstead Mortgage Trust III notes, 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.