COMPENSATION PROGRAMS - Other Compensation Programs (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Programs [Line Items]
Short-term incentive compensation program accruals	$ 1,400,000
Annual incentive compensation expense	1,200,000cmo_AnnualIncentiveCompensationExpense	2,800,000cmo_AnnualIncentiveCompensationExpense	4,100,000cmo_AnnualIncentiveCompensationExpense
DER issued and outstanding (in shares)	654
Dividend Equivalent Rights Payable	222,000cmo_DividendEquivalentRightsPayable
DER expense for the period	889,000us-gaap_DividendsShareBasedCompensation	811,000us-gaap_DividendsShareBasedCompensation	914,000us-gaap_DividendsShareBasedCompensation
Stock Options [Member]
Share Based Compensation Programs [Line Items]
Share awards contractual term	10 years
Options exercisable, weighted average remaining contractual term	3 years 6 months
Options exercisable, intrinsic value	26,000
Intrinsic value of option awards exercised	$ 67,000	$ 26,000	$ 620,000
Long-Term Equity-Based Awards [Member]
Share Based Compensation Programs [Line Items]
Issuance of common shares pursuant to future equity-based awards (in shares)	5,000,000
Common shares available for future issuance	4,927,763
Share awards contractual term	3 years
Share awards vesting period	3 years

Annual incentive compensation expense during the period.

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- Definition

Annual incentive compensation payable at the end of the period.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Period after which an equity-based payment arrangement expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- 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.

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- 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

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ 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)(3)

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

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- 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

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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

+ References

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- Definition

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ 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 (d)(2)

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

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