Unsecured Borrowings (Schedule Of Subordinated Note Balances And Related Weighted Average Interest Rate) (Details) (USD $) In Thousands, unless otherwise specified														12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Capstead Mortgage Trust I [Member]		Dec. 31, 2010 Capstead Mortgage Trust I [Member]	Dec. 31, 2011 Capstead Mortgage Trust II [Member]		Dec. 31, 2010 Capstead Mortgage Trust II [Member]	Dec. 31, 2011 Capstead Mortgage Trust III [Member]		Dec. 31, 2010 Capstead Mortgage Trust III [Member]	Dec. 31, 2011 For Final Twenty Years [Member]
Debt Instrument [Line Items]
Junior subordinated notes, Borrowings Outstanding	$ 103,095		$ 103,095		$ 36,083		$ 36,083	$ 41,238		$ 41,238	$ 25,774		$ 25,774
Unsecured borrowings, average rate	8.49%	[1]	8.49%	8.49%	8.31%	[1]	8.31%	8.46%	[1]	8.46%	8.78%	[1]	8.78%
Effective borrowing rate considering cash-flow hedges														7.56%

[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.