Represents the percentage of extension fee to be paid for exercising the option of extending the maturity term.

No definition available.

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Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the fixed charge coverage ratio as of the balance sheet date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the fixed charge coverage ratio as per the financial covenant, defined as adjusted consolidated earnings before interest, taxes, depreciation and amortization to consolidated fixed charges.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
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- Definition

Represents the leverage ratio as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cor_DebtInstrumentLeverageRatio
Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of options to extend the mortgage loan term.

+ References

No definition available.

+ Details

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Namespace Prefix:	cor_
Data Type:	xbrli:integerItemType
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- Definition

Represents the secured debt ratio as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the secured debt ratio defined as consolidated total secured debt to total gross asset value as per the financial covenant.

+ References

No definition available.

+ Details

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Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the unhedged variable rate debt ratio as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the increased maximum borrowing capacity allowed as per the accordion feature under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility ("accordion option").

+ References

No definition available.

+ Details

Name:	cor_LineOfCreditFacilityIncreasedMaximumBorrowingCapacityAccordionFeature
Namespace Prefix:	cor_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

+ Details

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

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Percentage of an entity's outstanding debt that is designated as a hedged item in cash flow, fair value, or net investment hedge.

+ References

No definition available.

+ Details

Name:	us-gaap_PercentageOfDebtHedgedByInterestRateDerivatives
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cor_SeniorUnsecuredRevolvingCreditFacilityMember
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- Details

Name:	dei_LegalEntityAxis=us-gaap_PartnershipInterestMember
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Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
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Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
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Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
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Data Type:	na
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Name:	us-gaap_VariableRateAxis=cor_DebtInstrumentVariableRateBasisLIBORMember
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Data Type:	na
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- Details

Name:	us-gaap_VariableRateAxis=cor_DebtInstrumentVariableRateBasisRateMember
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Name:	us-gaap_LongtermDebtTypeAxis=cor_RevolvingCreditFacilityPriorFacilityMember
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Name:	us-gaap_LongtermDebtTypeAxis=cor_SeniorUnsecuredTermLoan2020Member
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Debt (Details) $ in Thousands		9 Months Ended
Debt (Details) $ in Thousands	Jan. 31, 2014 USD ($)	Sep. 30, 2015 USD ($) item	Jun. 24, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt
Total principal outstanding		$ 360,250		$ 318,500
Credit Agreement \| Operating partnership
Debt
Commitment under the credit agreement		$ 500,000	$ 500,000
Number of options available for extensions \| item		1
Extension fee (as a percent)		0.10%
Revolving Credit Facility
Debt
Interest rate as of reporting date (as a percent)		1.75%		2.17%
Total principal outstanding		$ 110,250		$ 218,500
Letters of credit outstanding		6,300
Amount available for borrowing under the facility		$ 233,400
Leverage ratio (as a percent)		17.50%
Secured debt ratio (as a percent)		0.00%
Fixed charge coverage ratio		9.3
Unhedged variable rate debt ratio (as a percent)		8.40%
Revolving Credit Facility \| Operating partnership
Debt
Commitment under the credit agreement			350,000
Increased commitment under accordion feature		$ 700,000
Revolving Credit Facility \| Minimum
Debt
Fixed charge coverage ratio, Covenant		1.70
Revolving Credit Facility \| Maximum
Debt
Leverage ratio (as a percent)		0.60%
Secured debt ratio, Covenant (as a percent)		0.40%
Unhedged variable rate debt ratio (as a percent)		0.30%
Revolving Credit Facility \| LIBOR \| Operating partnership
Debt
Reference rate		LIBOR
Interest rate margin (as a percent)		1.55%
Leverage ratio (as a percent)		17.50%
Revolving Credit Facility \| LIBOR \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)		1.55%
Revolving Credit Facility \| LIBOR \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		2.25%
Revolving Credit Facility \| Base rate \| Operating partnership
Debt
Reference rate		base rate
Revolving Credit Facility \| Base rate \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)		0.55%
Revolving Credit Facility \| Base rate \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		1.25%
Revolving Credit Facility Prior Facility
Debt
Commitment under the credit agreement			405,000
2020 Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)		2.32%
Total principal outstanding		$ 150,000
Percentage of debt hedged		50.00%
Interest rate margin (as a percent)		2.93%
Amount available for borrowing under the facility		$ 75,000
2020 Senior Unsecured Term Loan \| Operating partnership
Debt
Unsecured term loan			$ 150,000
Leverage ratio (as a percent)		17.50%
2020 Senior Unsecured Term Loan \| LIBOR \| Operating partnership
Debt
Interest rate margin (as a percent)		1.75%
2020 Senior Unsecured Term Loan \| LIBOR \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)		1.75%
2020 Senior Unsecured Term Loan \| LIBOR \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		2.65%
2020 Senior Unsecured Term Loan \| Base rate \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)		0.75%
2020 Senior Unsecured Term Loan \| Base rate \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		1.65%
2019 Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)		3.23%		3.23%
Total principal outstanding		$ 100,000		$ 100,000
2019 Senior Unsecured Term Loan \| Operating partnership
Debt
Commitment under the credit agreement	$ 150,000
Term of loan facility	5 years
2019 Senior Unsecured Term Loan \| LIBOR \| Operating partnership
Debt
Reference rate	LIBOR	LIBOR
Interest rate margin (as a percent)		1.50%
Leverage ratio (as a percent)		17.50%
2019 Senior Unsecured Term Loan \| LIBOR \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)	1.50%
2019 Senior Unsecured Term Loan \| LIBOR \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)	2.20%
2019 Senior Unsecured Term Loan \| Base rate \| Operating partnership
Debt
Reference rate	base rate
2019 Senior Unsecured Term Loan \| Base rate \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)	0.50%
2019 Senior Unsecured Term Loan \| Base rate \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)	1.20%