CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$ 140,820us-gaap_NetIncomeLoss	$ 126,487us-gaap_NetIncomeLoss	$ 163,626us-gaap_NetIncomeLoss
Noncash items:
Amortization of investment premiums	101,872	125,872	96,677
Amortization of equity-based awards	2,390us-gaap_ShareBasedCompensation	2,201us-gaap_ShareBasedCompensation	2,236us-gaap_ShareBasedCompensation
Other depreciation and amortization	137	162	195
Incentive compensation paid in shares of common stock	0cmo_IncentiveCompensationPaidInStock	0cmo_IncentiveCompensationPaidInStock	2,799cmo_IncentiveCompensationPaidInStock
Change in measureable hedge ineffectiveness related to interest rate swap agreements designated as cash flow hedges	76us-gaap_UnrealizedGainLossOnDerivatives	(168)us-gaap_UnrealizedGainLossOnDerivatives	(411)us-gaap_UnrealizedGainLossOnDerivatives
Gain on sales of foreclosed real estate	0	0	(273)
Net change in receivables, other assets, accounts payable and accrued expenses	3,517	6,658	(919)
Net cash provided by operating activities	248,812	261,212	263,930
Investing activities:
Purchases of residential mortgage investments	(3,307,963)	(3,326,345)	(4,384,866)
Interest receivable acquired with the purchase of residential mortgage investments	(5,313)	(5,559)	(7,180)
Proceeds from sales of foreclosed real estate	0	0	2,010
Principal collections on residential mortgage investments, including changes in mortgage securities principal remittance receivable	2,785,337	3,516,634	2,756,772
Net cash (used in) provided by investing activities	(527,939)	184,730	(1,633,264)
Financing activities:
Proceeds from repurchase arrangements and similar borrowings	128,594,880	136,909,245	127,808,676
Principal payments on repurchase arrangements and similar borrowings	(128,270,935)	(137,210,576)	(126,376,876)
(Increase) decrease in cash collateral receivable from interest rate swap counterparties	(27,637)	24,470	(1,467)
Cash paid to redeem convertible preferred stock	0	(207,033)	0
Common stock repurchases	0	(7,292)	(35,062)
Proceeds from capital raising activities:
Issuance of preferred stock	18,180	165,756	4,479
Issuance of common stock	0	0	142,035
Other capital stock transactions	(468)cmo_OtherCapitalStockTransactions	(410)cmo_OtherCapitalStockTransactions	(585)cmo_OtherCapitalStockTransactions
Dividends paid	(140,723)us-gaap_PaymentsOfDividends	(132,191)us-gaap_PaymentsOfDividends	(173,138)us-gaap_PaymentsOfDividends
Net cash provided by (used in) financing activities	173,297	(458,031)	1,368,062
Net change in cash and cash equivalents	(105,830)	(12,089)	(1,272)
Cash and cash equivalents at beginning of year	413,356	425,445	426,717
Cash and cash equivalents at end of year	$ 307,526	$ 413,356	$ 425,445

Incentive compensation paid in stock that fully vests when granted.

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The change in cash remitted to swap counterparties to meet initial and ongoing margin requirements that are based on the fair value of the swap agreements.

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The cash inflow from the issuance of common stock, preferred stock, treasury stock, stock options, and other types of equity, net of other miscellaneous stock related outflows.

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Purchased Interest Receivable Related To Purchases Of Residential Mortgage Investments

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

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The aggregate net amount of depreciation, amortization, and accretion recognized during an accounting period. As a noncash item, the net amount is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Other cash or noncash adjustments to reconcile net income to cash provided by (used in) operating activities that are not separately disclosed in the statement of cash flows (for example, cash received or cash paid during the current period for miscellaneous operating activities, net change during the reporting period in other assets or other liabilities).

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The cash outflow to reacquire common stock during the period.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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The cash inflow from the additional capital contribution to the entity.

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Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholders and which takes precedence over common stockholders in the event of liquidation.

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