Accounting Policies	12 Months Ended
Dec. 31, 2011
Accounting Policies [Abstract]
Accounting Policies	NOTE 2 — ACCOUNTING POLICIES *Basis of Presentation* The consolidated financial statements include the accounts of Capstead Mortgage Corporation and its wholly-owned and majority-owned subsidiaries over which it exercises control. Capstead also consolidates, if appropriate, any variable interest entities in which the Company holds an interest. With the October 2009 acquisition of a senior lien to its existing subordinated loans to two townhome developments in the Dallas, Texas area, the Company began consolidating the entities that owned the underlying real estate. In November 2011 the Company foreclosed on the properties, assuming ownership of the remaining unsold townhomes. The common securities held by Capstead in statutory trusts organized by the Company to issue long-term unsecured borrowings are not considered variable interests at risk pursuant to variable interest entity accounting principles. Capstead accounts for these investments under the equity method of accounting. Investments in unconsolidated affiliates are initially recorded at cost and subsequently adjusted for Capstead's equity in earnings and losses and cash contributions and distributions. Intercompany balances and transactions have been eliminated. Certain prior year amounts have been reclassified to conform to the current year presentation. *Recent Accounting Developments* In June 2011, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") 2011-05, "Comprehensive Income (Topic 220): Presentation of Comprehensive Income." ASU 2011-05 amends Accounting Standards Codification ("ASC") Topic 220, Comprehensive Income, to require that all non-owner changes in stockholders' equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements, and it eliminates the option to present components of other comprehensive income as a part of the statement of changes in stockholders' equity. In addition, ASU 2011-05 requires an entity to present on the face of the financial statements reclassification adjustments for items that are reclassified from other comprehensive income to net income in the statement(s) where the components of net income and the components of other comprehensive income are presented. These amendments are to be applied retrospectively and, except for presentation requirements on the statement of income for reclassification adjustments which have been deferred, are effective for fiscal years, and interim periods within those years, beginning after December 15, 2011 with early adoption allowed. The Company elected to adopt ASU 2011-05 for the fiscal year ended 2011. The adoption of ASU 2011-05 did not impact the Company's financial position or results of operations, as it only requires a change in the format of the current presentation. *Use of Estimates* The use of estimates is inherent in the preparation of financial statements. Amortization of investment premiums on financial assets is based on estimates of future mortgage prepayments, which are impacted by future changes in interest rates and other factors. Actual results could differ from those estimates, which could adversely affect earnings. Fair values of financial instruments are estimated using available market information and appropriate valuation methodologies; however, considerable judgment is required in interpreting market data to develop these estimates. Fair values fluctuate on a daily basis and are influenced by changes in, and market expectations for changes in, interest rates, market liquidity conditions and levels of mortgage prepayments, as well as other factors. Accordingly, estimates of fair value are as of the balance sheet dates and are not necessarily indicative of the amounts that could be realized in a current market exchange. The use of different market assumptions and estimation methodologies may have a material effect on estimated fair values. Considerable judgment is also exercised in making impairment conclusions and estimating impairment charges. *Cash and Cash Equivalents* Cash and cash equivalents include unrestricted cash on hand and highly liquid investments with original maturities of three months or less when purchased. *Financial Assets* Most of Capstead's financial assets are mortgage securities classified as available-for-sale and carried at fair value with unrealized gains and losses reported as a separate component of Accumulated other comprehensive income (loss). Loans classified as held for investment or mortgage securities classified as held-to-maturity are carried at amortized cost (unpaid principal balance, adjusted for unamortized investment premiums and discounts). Interest is recorded as income when earned, unless an investment has been placed on nonaccrual status. Placing investments in loans on nonaccrual status, charging off uncollectable loans, resuming the accrual of interest, and determining the appropriate accounting treatment for related cash receipts is determined on a case-by-case basis. Investment premiums and discounts are recognized as adjustments to interest income by the interest method, generally over the expected life of the related financial assets. Realized gains and losses from sales are recorded as a component of Miscellaneous other revenue (expense). The specific identification method is used to determine the cost of financial assets sold. Financial assets are reviewed for potential impairment at each balance sheet date. Other-than-temporary impairments of investments in mortgage securities can occur with adverse changes in the financial condition of the issuer and changes in the Company's intent or ability to hold the security until any declines in fair value are recovered. The amount of any such other-than-temporary impairment for an investment in a mortgage security is measured by comparing the recorded amount of the security to its fair value. An investment in a loan is considered impaired if it becomes probable that the Company will be unable to collect all amounts due according to the loan's contractual terms and the amount of any impairment is measured by comparing the recorded amount of the loan to the present value of expected cash flows. Impairment charges are recorded as a component of Miscellaneous other revenue (expense). *Borrowings* Borrowings are carried at amortized cost (unpaid principal balances, net of unamortized discounts and premiums, when present). Discounts and premiums, as well as debt issue costs, which are recorded in Receivables and other assets, are recognized as adjustments to interest expense by the interest method over the term of the related borrowings. Borrowings under repurchase arrangements create exposure to the potential for failure on the part of counterparties to honor their commitment to return pledged collateral. In the event of a default by a counterparty, the Company may have difficulty recovering its collateral. To mitigate this risk, the Company monitors the creditworthiness of its counterparties and manages its exposure to any single counterparty. *Derivative Financial Instruments ("Derivatives")* Derivatives used by Capstead for risk management purposes are carried at fair value as assets or liabilities. The accounting for changes in fair value of each Derivative held depends on whether it has been designated as a hedge for accounting purposes, as well as the type of hedging relationship identified. Capstead will typically designate any Derivatives held as cash flow hedges. To qualify as a cash flow hedge, at the inception of the hedge relationship the Company must document that the hedge relationship is anticipated to be highly effective and monitor ongoing effectiveness on at least a quarterly basis. As long as the hedge relationship remains effective, the effective portion of changes in fair value of the Derivative are recorded in Accumulated other comprehensive income (loss) and the ineffective portion is recorded in interest expense. Changes in fair value of Derivatives not held as accounting hedges, or for which the hedge relationship is no longer considered highly effective, are recorded in Miscellaneous other revenue (expense). Holding Derivatives creates exposure to credit risk related to the potential for failure on the part of counterparties to honor their commitments. In addition, the Company is required to post collateral based on any declines in the market value of the Derivatives. In the event of default by a counterparty, the Company may have difficulty recovering its collateral and may not receive payments provided for under the terms of the Derivative. To mitigate this risk, the Company uses only well-established commercial banks as counterparties. The Company uses interest rate swap agreements in cash flow hedge relationships in order to hedge variability in borrowing rates due to changes in the underlying benchmark interest rate related to a designated portion of its current and anticipated future borrowings. Variable-rate swap payments to be received and any measured hedge ineffectiveness are recorded in interest expense as an offset to interest owed on the hedged borrowings that reset to market rates generally every 30 to 90 days. Fixed-rate swap payments to be made are also recorded in interest expense. The combination of these cash flows results in a relatively fixed rate on these borrowings, subject to certain adjustments. Cash collateral receivable from interest rate swap counterparties represents cash remitted to swap counterparties to meet initial and ongoing margin requirements that are based on the fair value of these agreements, including related interest receivable or payable under the terms of the agreements. The Company may also remit mortgage securities to certain of its swap counterparties to meet ongoing margin requirements. Such mortgage securities, if any, are included in Mortgage securities and similar investments. Similarly, Cash collateral payable to interest rate swap counterparties represents cash received from counterparties to meet margin call requirements. For presentation purposes, the Company does not offset individual counterparty collateral receivables (or payables) with the recorded fair value of related interest rate swap agreements pursuant to master netting arrangements. In addition, gross unrealized gains on Derivatives (recorded as assets) are stated separately from gross unrealized losses (recorded as liabilities) without regard to counterparty. *Equity-based Compensation* Equity-based compensation cost is measured at grant date, based on the fair value of the award, and is recognized as an expense over the related requisite service period. The Company recognizes compensation cost for option awards on a straightline basis over the requisite service period for each portion of an award that vests separately. Compensation cost for stock awards subject only to service conditions is recognized on a straightline basis over the requisite service period for the entire award. Compensation cost for stock awards subject to performance conditions is recognized on a straightline basis over the requisite service period for each portion of the award that vests separately, subject to achieving the related performance conditions. *Income Taxes* Capstead Mortgage Corporation and its qualified REIT subsidiaries ("Capstead REIT") have elected to be taxed as a REIT. As a result, Capstead REIT is not taxed on taxable income distributed to stockholders if certain REIT qualification tests are met. Capstead's policy is to distribute 100% of the taxable income of the REIT, after application of available tax attributes, within the time limits prescribed by the Internal Revenue Code (the "Code"), which may extend into the subsequent taxable year. The Company may find it advantageous from time to time to elect taxable REIT subsidiary status for certain of its subsidiaries in which case taxable income of any such subsidiary would be subject to federal and, where applicable, state or local income taxes. Any such income taxes are accounted for using the liability method. Related deferred income tax assets and liabilities are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has not recognized any liabilities for unrecognized tax benefits using a "more likely than not" threshold for the recognition and measurement of the financial statement effects of tax positions taken on a tax return filing. Should any such liabilities be recognized in future periods, the Company will record related interest and penalties in Other general and administrative expense. *Dividend Classification* Capstead records common and preferred share dividends in the Accumulated deficit component of Stockholders' equity only to the extent of available earnings for the related quarterly or monthly period. Any dividends declared in excess of available earnings are considered returns of capital for financial reporting purposes and are recorded as reductions of Paid-in capital. The tax and financial reporting classification of dividends can differ primarily as a result of differences between taxable income and Net income and how taxable income is allocated to dividends paid.

NOTE 2 — ACCOUNTING POLICIES

Basis of Presentation

The consolidated financial statements include the accounts of Capstead Mortgage Corporation and its wholly-owned and majority-owned subsidiaries over which it exercises control. Capstead also consolidates, if appropriate, any variable interest entities in which the Company holds an interest. With the October 2009 acquisition of a senior lien to its existing subordinated loans to two townhome developments in the Dallas, Texas area, the Company began consolidating the entities that owned the underlying real estate. In November 2011 the Company foreclosed on the properties, assuming ownership of the remaining unsold townhomes. The common securities held by Capstead in statutory trusts organized by the Company to issue long-term unsecured borrowings are not considered variable interests at risk pursuant to variable interest entity accounting principles. Capstead accounts for these investments under the equity method of accounting. Investments in unconsolidated affiliates are initially recorded at cost and subsequently adjusted for Capstead's equity in earnings and losses and cash contributions and distributions. Intercompany balances and transactions have been eliminated. Certain prior year amounts have been reclassified to conform to the current year presentation.

Recent Accounting Developments

In June 2011, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") 2011-05, "Comprehensive Income (Topic 220): Presentation of Comprehensive Income." ASU 2011-05 amends Accounting Standards Codification ("ASC") Topic 220, Comprehensive Income, to require that all non-owner changes in stockholders' equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements, and it eliminates the option to present components of other comprehensive income as a part of the statement of changes in stockholders' equity. In addition, ASU 2011-05 requires an entity to present on the face of the financial statements reclassification adjustments for items that are reclassified from other comprehensive income to net income in the statement(s) where the components of net income and the components of other comprehensive income are presented. These amendments are to be applied retrospectively and, except for presentation requirements on the statement of income for reclassification adjustments which have been deferred, are effective for fiscal years, and interim periods within those years, beginning after December 15, 2011 with early adoption allowed. The Company elected to adopt ASU 2011-05 for the fiscal year ended 2011. The adoption of ASU 2011-05 did not impact the Company's financial position or results of operations, as it only requires a change in the format of the current presentation.

Use of Estimates

The use of estimates is inherent in the preparation of financial statements. Amortization of investment premiums on financial assets is based on estimates of future mortgage prepayments, which are impacted by future changes in interest rates and other factors. Actual results could differ from those estimates, which could adversely affect earnings. Fair values of financial instruments are estimated using available market information and appropriate valuation methodologies; however, considerable judgment is required in interpreting market data to develop these estimates. Fair values fluctuate on a daily basis and are influenced by changes in, and market expectations for changes in, interest rates, market liquidity conditions and levels of mortgage prepayments, as well as other factors. Accordingly, estimates of fair value are as of the balance sheet dates and are not necessarily indicative of the amounts that could be realized in a current market exchange. The use of different market assumptions and estimation methodologies may have a material effect on estimated fair values. Considerable judgment is also exercised in making impairment conclusions and estimating impairment charges.

Cash and Cash Equivalents

Cash and cash equivalents include unrestricted cash on hand and highly liquid investments with original maturities of three months or less when purchased.

Financial Assets

Most of Capstead's financial assets are mortgage securities classified as available-for-sale and carried at fair value with unrealized gains and losses reported as a separate component of Accumulated other comprehensive income (loss). Loans classified as held for investment or mortgage securities classified as held-to-maturity are carried at amortized cost (unpaid principal balance, adjusted for unamortized investment premiums and discounts). Interest is recorded as income when earned, unless an investment has been placed on nonaccrual status. Placing investments in loans on nonaccrual status, charging off uncollectable loans, resuming the accrual of interest, and determining the appropriate accounting treatment for related cash receipts is determined on a case-by-case basis. Investment premiums and discounts are recognized as adjustments to interest income by the interest method, generally over the expected life of the related financial assets. Realized gains and losses from sales are recorded as a component of Miscellaneous other revenue (expense). The specific identification method is used to determine the cost of financial assets sold.

Financial assets are reviewed for potential impairment at each balance sheet date. Other-than-temporary impairments of investments in mortgage securities can occur with adverse changes in the financial condition of the issuer and changes in the Company's intent or ability to hold the security until any declines in fair value are recovered. The amount of any such other-than-temporary impairment for an investment in a mortgage security is measured by comparing the recorded amount of the security to its fair value. An investment in a loan is considered impaired if it becomes probable that the Company will be unable to collect all amounts due according to the loan's contractual terms and the amount of any impairment is measured by comparing the recorded amount of the loan to the present value of expected cash flows. Impairment charges are recorded as a component of Miscellaneous other revenue (expense).

Borrowings

Borrowings are carried at amortized cost (unpaid principal balances, net of unamortized discounts and premiums, when present). Discounts and premiums, as well as debt issue costs, which are recorded in Receivables and other assets, are recognized as adjustments to interest expense by the interest method over the term of the related borrowings. Borrowings under repurchase arrangements create exposure to the potential for failure on the part of counterparties to honor their commitment to return pledged collateral. In the event of a default by a counterparty, the Company may have difficulty recovering its collateral. To mitigate this risk, the Company monitors the creditworthiness of its counterparties and manages its exposure to any single counterparty.

Derivative Financial Instruments ("Derivatives")

Derivatives used by Capstead for risk management purposes are carried at fair value as assets or liabilities. The accounting for changes in fair value of each Derivative held depends on whether it has been designated as a hedge for accounting purposes, as well as the type of hedging relationship identified. Capstead will typically designate any Derivatives held as cash flow hedges. To qualify as a cash flow hedge, at the inception of the hedge relationship the Company must document that the hedge relationship is anticipated to be highly effective and monitor ongoing effectiveness on at least a quarterly basis. As long as the hedge relationship remains effective, the effective portion of changes in fair value of the Derivative are recorded in Accumulated other comprehensive income (loss) and the ineffective portion is recorded in interest expense. Changes in fair value of Derivatives not held as accounting hedges, or for which the hedge relationship is no longer considered highly effective, are recorded in Miscellaneous other revenue (expense). Holding Derivatives creates exposure to credit risk related to the potential for failure on the part of counterparties to honor their commitments. In addition, the Company is required to post collateral based on any declines in the market value of the Derivatives. In the event of default by a counterparty, the Company may have difficulty recovering its collateral and may not receive payments provided for under the terms of the Derivative. To mitigate this risk, the Company uses only well-established commercial banks as counterparties.

The Company uses interest rate swap agreements in cash flow hedge relationships in order to hedge variability in borrowing rates due to changes in the underlying benchmark interest rate related to a designated portion of its current and anticipated future borrowings. Variable-rate swap payments to be received and any measured hedge ineffectiveness are recorded in interest expense as an offset to interest owed on the hedged borrowings that reset to market rates generally every 30 to 90 days. Fixed-rate swap payments to be made are also recorded in interest expense. The combination of these cash flows results in a relatively fixed rate on these borrowings, subject to certain adjustments.

Cash collateral receivable from interest rate swap counterparties represents cash remitted to swap counterparties to meet initial and ongoing margin requirements that are based on the fair value of these agreements, including related interest receivable or payable under the terms of the agreements. The Company may also remit mortgage securities to certain of its swap counterparties to meet ongoing margin requirements. Such mortgage securities, if any, are included in Mortgage securities and similar investments. Similarly, Cash collateral payable to interest rate swap counterparties represents cash received from counterparties to meet margin call requirements. For presentation purposes, the Company does not offset individual counterparty collateral receivables (or payables) with the recorded fair value of related interest rate swap agreements pursuant to master netting arrangements. In addition, gross unrealized gains on Derivatives (recorded as assets) are stated separately from gross unrealized losses (recorded as liabilities) without regard to counterparty.

Equity-based Compensation

Equity-based compensation cost is measured at grant date, based on the fair value of the award, and is recognized as an expense over the related requisite service period. The Company recognizes compensation cost for option awards on a straightline basis over the requisite service period for each portion of an award that vests separately. Compensation cost for stock awards subject only to service conditions is recognized on a straightline basis over the requisite service period for the entire award. Compensation cost for stock awards subject to performance conditions is recognized on a straightline basis over the requisite service period for each portion of the award that vests separately, subject to achieving the related performance conditions.

Income Taxes

Capstead Mortgage Corporation and its qualified REIT subsidiaries ("Capstead REIT") have elected to be taxed as a REIT. As a result, Capstead REIT is not taxed on taxable income distributed to stockholders if certain REIT qualification tests are met. Capstead's policy is to distribute 100% of the taxable income of the REIT, after application of available tax attributes, within the time limits prescribed by the Internal Revenue Code (the "Code"), which may extend into the subsequent taxable year. The Company may find it advantageous from time to time to elect taxable REIT subsidiary status for certain of its subsidiaries in which case taxable income of any such subsidiary would be subject to federal and, where applicable, state or local income taxes. Any such income taxes are accounted for using the liability method. Related deferred income tax assets and liabilities are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has not recognized any liabilities for unrecognized tax benefits using a "more likely than not" threshold for the recognition and measurement of the financial statement effects of tax positions taken on a tax return filing. Should any such liabilities be recognized in future periods, the Company will record related interest and penalties in Other general and administrative expense.

Dividend Classification

Capstead records common and preferred share dividends in the Accumulated deficit component of Stockholders' equity only to the extent of available earnings for the related quarterly or monthly period. Any dividends declared in excess of available earnings are considered returns of capital for financial reporting purposes and are recorded as reductions of Paid-in capital. The tax and financial reporting classification of dividends can differ primarily as a result of differences between taxable income and Net income and how taxable income is allocated to dividends paid.