ACCOUNTING POLICIES (Policies)	12 Months Ended
ACCOUNTING POLICIES (Policies)	Dec. 31, 2013
ACCOUNTING POLICIES [Abstract]
Basis of Presentation	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 it holds an interest. Common securities held by the Company in statutory trusts organized to issue long-term unsecured borrowings (prior to the dissolution of these trusts in December 2013 – see NOTE 5) were not considered variable interests at risk pursuant to variable interest entity accounting principles and were accounted for as investments in unconsolidated affiliates. Investments in any unconsolidated affiliates are initially recorded at cost and subsequently adjusted for the Company’s equity in earnings and losses and cash contributions and distributions. Intercompany balances and transactions have been eliminated. Prior year amounts included in financing activities in the Statement of Cash Flows pertaining to capital stock transactions have been reclassified to conform to the current year presentation. Additionally, prior year compensation costs related to dividend equivalent rights (see NOTE 12) have been reclassified from Salaries and benefits to Short-term incentive compensation in the Statement of Income.
Recent Accounting Developments	Recent Accounting Developments In December 2011 the Financial Accounting Standards Board (“FASB”) issued ASU No. 2011-11, Disclosures about Offsetting Assets and Liabilities. In January 2013, the FASB issued ASU No. 2013-01, Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. The Company adopted the requirements of ASU No. 2011-11 as amended by ASU No. 2013-01 with its first quarterly filing in 2013. In February 2013 the FASB issued Accounting Standards Update (“ASU”) No. 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income that amended ASU No. 2011-12 and ASU No. 2011-05. The Company adopted the requirements of ASU No. 2013-02 with its first quarterly filing in 2013. The provisions of these ASUs are all disclosure-related and as such, their adoption by the Company had no effect on its results of operations, financial condition, or cash flows.
Use of Estimates	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 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	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. 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. 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. Impairment charges are recorded as a component of Miscellaneous other revenue (expense).
Borrowings	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")	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 is recorded in Accumulated other comprehensive income and the ineffective portion is recorded in interest expense. The effective portion of changes in fair value is reclassified from Accumulated comprehensive income to earnings over the term of the Derivative primarily in the form of Derivative cash flows that are either in excess of or lower than market rates. Changes in fair value of Derivatives not held as accounting hedges, if any, 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. These adjustments include changes in spreads between variable rates on the swap agreements and actual borrowing rates as well as the effects of measured hedge ineffectiveness. 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 Derivatives, 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 Residential mortgage 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 Equity-based compensation cost is measured at the fair value of the awards on the grant date and recognized as expense over the related requisite service or performance measurement periods. Compensation cost for option awards is recognized on a straight-line 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 straight-line basis over the requisite service period for the awards. Compensation cost for stock awards and restricted stock units subject to performance conditions is recognized on a straight-line basis over the requisite measurement periods, subject to achieving the related performance conditions.
Income Taxes	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	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 period. Any dividends declared in excess of available earnings are considered a return 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.