Agreement period of LIBOR interest rate, in PnYnMnDTnHnMnS' format.

No definition available.

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- Definition

Average interest rate on new forward-starting SWAP agreements entered into during period specified by the derivative(s).

+ References

No definition available.

+ Details

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- Definition

Average interest rate on SWAP agreements expiring during period specified by the derivative(s).

+ References

No definition available.

+ Details

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- Definition

Aggregate notional amount entered into during period specified by the derivative(s). Expressed as an absolute value.

+ References

No definition available.

+ Details

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- Definition

Aggregate notional amount expiring during period specified by the derivative(s). Expressed as an absolute value.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmo_
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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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Period Type:	instant

- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

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- Details

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- Details

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- Details

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- Details

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- Details

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USE OF DERIVATIVES, OFFSETTING DISCLOSURES AND CHANGES IN OTHER COMPREHENSIVE INCOME BY COMPONENT- Schedule of Swap Agreements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2010	Dec. 31, 2014
Notional Disclosures [Abstract]
Notional Amount	$ 8,400,000
Derivative instruments unrealized losses to be recognized	5,600
Interest Rate SWAP Currently-Paying Contracts [Member]
Notional Disclosures [Abstract]
Notional Amount	8,100,000
Interest Rate SWAP Currently-Paying Contracts [Member] \| First Quarter 2016 (Expired January 4, 2016) [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 1,700,000
Average Fixed Rate Payment Requirement	0.51%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Second Quarter 2016 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 1,100,000
Average Fixed Rate Payment Requirement	0.47%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Third Quarter 2016 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 700,000
Average Fixed Rate Payment Requirement	0.56%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Fourth Quarter 2016 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 800,000
Average Fixed Rate Payment Requirement	0.66%
Interest Rate SWAP Currently-Paying Contracts [Member] \| First Quarter 2017 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 1,000,000
Average Fixed Rate Payment Requirement	0.72%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Second Quarter 2017 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 900,000
Average Fixed Rate Payment Requirement	0.74%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Third Quarter 2017 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 400,000
Average Fixed Rate Payment Requirement	0.74%
Interest Rate SWAP Currently-Paying Contracts [Member] \| Fourth Quarter 2017 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 1,500,000
Average Fixed Rate Payment Requirement	0.79%
Interest Rate SWAP Forward-Starting Contracts [Member] \| First Quarter 2018 [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 300,000
Average Fixed Rate Payment Requirement	0.92%
Interest Rate Swap Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
SWAP agreement notional amount during period	$ 3,600,000	$ 100,000
SWAP agreement average interest rate during period	0.77%	4.09%
Swap agreement notional amount expiring during period	$ 2,900,000
SWAP agreement average interest rate expiring during period	0.47%
Notional Disclosures [Abstract]
Payment term of LIBOR interest rate agreement	2 years	20 years
Accrued interest	$ 10,900		$ 9,500
Interest Rate Swap Expired One [Member]
Notional Disclosures [Abstract]
Payment term of LIBOR interest rate agreement	2 years
Repurchase Arrangements and Similar Borrowings [Member]
Notional Disclosures [Abstract]
Accrued interest	$ 9,300		$ 6,100