COMPENSATION PROGRAMS - Other Compensation Programs (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Programs [Line Items]
Short-term incentive compensation program accruals	$ 489,000
Annual incentive compensation expense	489,000cmo_AnnualIncentiveCompensationExpense	318,000cmo_AnnualIncentiveCompensationExpense
DER issued and outstanding (in shares)	654,000
Dividend Equivalent Rights Payable	203,000cmo_DividendEquivalentRightsPayable
DER expense for the period	$ 203,000us-gaap_DividendsShareBasedCompensation	$ 222,000us-gaap_DividendsShareBasedCompensation
Targeted award opportunity on base salary	125.00%
Long-Term Equity-Based Awards [Member]
Share Based Compensation Programs [Line Items]
Common shares available for future issuances	4,432,739
Share awards vesting period	3 years

Annual incentive compensation expense during the period.

No definition available.

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Namespace Prefix:	cmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Annual incentive compensation payable at the end of the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Gross number of dividend equivalent rights granted outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cmo_DividendEquivalentRightsAwardedOutstanding
Namespace Prefix:	cmo_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the Dividend Equivalent Rights payable at the end of the period.

+ References

No definition available.

+ Details

Name:	cmo_DividendEquivalentRightsPayable
Namespace Prefix:	cmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Refers to officer has a targeted award opportunity percentage on his base salary.

+ References

No definition available.

+ Details

Name:	cmo_TargetedAwardOpportunityOnBaseSalary
Namespace Prefix:	cmo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared and applicable to holders of share-based compensation, for example, but not limited to, non-vested shares, stock options, or restricted stock units.

+ References

No definition available.

+ Details

Name:	us-gaap_DividendsShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: