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

No definition available.

Name:	cor_DebtInstrumentExtensionOfMaturityTermExtensionFeePercentage
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

Name:	cor_DebtInstrumentFixedChargeCoverageRatio
Namespace Prefix:	cor_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- 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

Name:	cor_DebtInstrumentNumberOfOptionsForExtensionOfTermOfMaturity
Namespace Prefix:	cor_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	cor_DebtInstrumentSecuredDebtRatio
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

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

- Definition

Represents the amount of increase in the Line of Credit Accordion Feature borrowing capacity.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

Name:	cor_LineOfCreditMaximumBorrowingCapacityIncludingAccordionFeature
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

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

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

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
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

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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

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

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

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=cor_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cor_SeniorUnsecuredTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cor_PriorFacilityMember
Namespace Prefix:
Data Type:	na
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Period Type:

Debt - Revolving Credit Facility (Details) $ in Millions	9 Months Ended
Debt - Revolving Credit Facility (Details) $ in Millions	Sep. 30, 2016 USD ($) item	Feb. 02, 2016 USD ($)	Jun. 24, 2015 USD ($)
Credit Agreement
Debt
Leverage ratio (as a percent)	20.70%
Secured debt ratio (as a percent)	0.00%
Fixed charge coverage ratio	8.1
Unhedged variable rate debt ratio (as a percent)	9.30%
Credit Agreement \| Minimum
Debt
Fixed charge coverage ratio	1.70
Credit Agreement \| Maximum
Debt
Leverage ratio (as a percent)	0.60%
Secured debt ratio (as a percent)	0.40%
Unhedged variable rate debt ratio (as a percent)	0.30%
Operating partnership \| LIBOR
Debt
Interest rate margin (as a percent)	1.55%
Operating partnership \| Credit Agreement
Debt
Number of options available for extensions \| item	1
Extension fee (as a percent)	0.10%
Maximum borrowing capacity		$ 600.0	$ 500.0
Unsecured term loan		100.0
Increase in accordion feature borrowing capacity		100.0
Maximum borrowing capacity including accordion feature		$ 800.0	700.0
Borrowing capacity at end of period	$ 350.0
Letters of credit outstanding	4.5
Amount available for borrowing under the facility	250.8
Operating partnership \| Credit Agreement \| Revolving Credit Facility
Debt
Maximum borrowing capacity			350.0
Borrowed and outstanding	$ 94.8
Leverage ratio (as a percent)	20.70%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)	1.55%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)	2.25%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)	0.55%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)	1.25%
Operating partnership \| Credit Agreement \| Senior Unsecured Term Loan
Debt
Unsecured term loan			150.0
Operating partnership \| Prior Facility
Debt
Maximum borrowing capacity			$ 405.0