The percentage of a participant's voluntary contribution the Company will match.

No definition available.

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

- Definition

Compensation plan of voluntary contribution addition

+ References

No definition available.

+ Details

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

- Definition

The maximum defined contribution compensation expense recognized during the period.

+ References

No definition available.

+ Details

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

- Definition

Number Of Years For Average Long Term Investment Capital

+ References

No definition available.

+ Details

Name:	cmo_NumberOfYearsForAverageLongTermInvestmentCapital
Namespace Prefix:	cmo_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Of Average Long Term Investment Capita

+ References

No definition available.

+ Details

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

- Definition

Percentage Of Performance-Based Awards Granted

+ References

No definition available.

+ Details

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

- Definition

Performance threshold multiplier, basis points.

+ References

No definition available.

+ Details

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

- Details

Name:	cmo_ShareBasedCompensationProgramsLineItems
Namespace Prefix:	cmo_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Spread Over Ten Year US Treasury Rate

+ References

No definition available.

+ Details

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

- Definition

The number of shares originally issued under a share based award plan pertaining to grants outstanding during the period on other than stock option plans (for example, phantom stock plan, stock appreciation rights plan, performance target plan).

+ References

No definition available.

+ Details

Name:	cmo_TotalGrants
Namespace Prefix:	cmo_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average remaining contractual term as of the balance sheet date for those share-based payment arrangements exercisable and outstanding.

+ References

No definition available.

+ Details

Name:	cmo_WeightedAverageRemainingContractualTerm
Namespace Prefix:	cmo_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 9

-Section 03

-Paragraph 15

-Subparagraph 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 15

-Subparagraph a

+ Details

Name:	us-gaap_DividendsPayableCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph h

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

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

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate amount of expenditures for salaries, wages, profit sharing and incentive compensation, and other employee benefits, including equity-based compensation, and pension and other postretirement benefit expense.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

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

- Definition

Other generally recurring costs associated with normal operations excluding those directly related to the marketing or selling of products and services not otherwise defined.

+ References

+ Details

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

- Definition

The date when the equity-based award expires as specified in the award agreement, which may be presented in a variety of ways (for example, year, month and year, day, month and year, quarter of a year).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

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

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardExpirationDating
Namespace Prefix:	us-gaap_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the period of time over 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, which may be expressed in a variety of ways (for example, in years, month and year).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod
Namespace Prefix:	us-gaap_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum vesting term over 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.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriodMaximum
Namespace Prefix:	us-gaap_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum vesting term over 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.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriodMinimum
Namespace Prefix:	us-gaap_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(1)(c), d(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iii)

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

+ Details

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

- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

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

+ Details

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

- Definition

As of the balance sheet date, the total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options that are exercisable.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph d(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(2)

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

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ 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 (c)(1)(iii)

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

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Compensation Programs (Narrative) (Details) (USD $)	3 Months Ended
Compensation Programs (Narrative) (Details) (USD $)	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Share Based Compensation Programs [Line Items]
Total grants	0	0
Expiration date of grant	July 1, 2014
Percentage of investment capital, maximum	10.00%
Common shares for future issuance	858,668
Salaries and benefits	$ 1,827,000	$ 1,700,000
Common stock dividend payable	40,301,000		38,184,000
Other Benefit Programs [Member]
Share Based Compensation Programs [Line Items]
Salaries and benefits	133,000	112,000
Compensation plan of voluntary contribution	50.00%
Compensation plan of voluntary contribution, maximum	6.00%
Compensation plan of voluntary contribution, additional	3.00%
Annual Incentive Compensation [Member]
Share Based Compensation Programs [Line Items]
Percentage of investment capital, maximum	10.00%
Number of years for average long-term investment capital	10
Spread over 10-year U.S. Treasury rate (basis points)	2.00%
Performance threshold multiplier, basis points	0.50%
Long-Term Equity-Based Awards [Member]
Share Based Compensation Programs [Line Items]
Percentage of investment capital, maximum	8.00%
Number of years for average long-term investment capital	10
Spread over 10-year U.S. Treasury rate (basis points)	2.00%
Share awards vesting period (in years)	three
Performance-Based Stock Awards Vesting In Three Year [Member]
Share Based Compensation Programs [Line Items]
Percentage of performance-based awards granted	50.00%
Performance-Based Stock Awards Vesting After Three Year [Member]
Share Based Compensation Programs [Line Items]
Percentage of performance-based awards granted	50.00%
Share awards vesting period, maximum (in years)	three
Share awards vesting period, minimum (in years)	one
Stock Awards Activity [Member]
Share Based Compensation Programs [Line Items]
Salaries and benefits	469,000	391,000
Other general and administrative expense	80,000	36,000
Common stock dividend payable	445,000
Total of unrecognized compensation expense for unvested option awards	4,200,000
Weighted average remaining contractual term (in years)	1.7
Option Awards [Member]
Share Based Compensation Programs [Line Items]
Share awards vesting period (in years)	ten
Weighted average remaining contractual term (in years)	5.2
Exercisable option awards outstanding	220,000
Weighted average exercise price	$ 10.82
Aggregate intrinsic value of stock options	518,000
Intrinsic value of option awards exercised	$ 125,000
2011 [Member]
Share Based Compensation Programs [Line Items]
Total grants	72,000
2011 [Member] \| Performance-Based Stock Awards [Member]
Share Based Compensation Programs [Line Items]
Total grants	132,490
Expiration date of grant	2018