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 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

Name:	cor_DebtInstrumentFixedChargeCoverageRatioCovenantCompliance
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 leverage ratio as per the financial covenant defined as consolidated total indebtedness to total gross asset value.

+ References

No definition available.

+ Details

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

+ References

No definition available.

+ Details

Name:	cor_DebtInstrumentSecuredRatioCovenantCompliance
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 unhedged variable rate debt ratio as per the financial covenant defined as unhedged variable indebtedness to gross asset value.

+ References

No definition available.

+ Details

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

- Definition

Represents the increase in the 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_LineOfCreditIncreaseMaximumBorrowingCapacityAccordionFeature
Namespace Prefix:	cor_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

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

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 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 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 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

+ Details

Name:	us-gaap_LineOfCredit
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

+ Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=cor_CreditAgreementMember
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:

Debt - Revolving Credit Facility (Details) $ in Millions			12 Months Ended
Debt - Revolving Credit Facility (Details) $ in Millions	Feb. 02, 2016 USD ($)	Jun. 24, 2015 USD ($) item	Dec. 31, 2016 USD ($)
Revolving Credit Facility
Debt
Maximum borrowing capacity			$ 350.0
Borrowed and outstanding			194.0
Letters of credit outstanding			4.5
Amount available for borrowing under the facility			$ 151.5
Leverage ratio (as a percent)			0.00%
Revolving Credit Facility \| LIBOR
Debt
Interest rate margin (as a percent)			1.55%
Reference rate			LIBOR
Revolving Credit Facility \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)			1.55%
Revolving Credit Facility \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)			2.25%
Revolving Credit Facility \| Base Rate
Debt
Reference rate			base rate
Revolving Credit Facility \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)			0.55%
Revolving Credit Facility \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)			1.25%
Credit Agreement
Debt
Number of options available for extensions \| item		1
Extension fee (as a percent)		0.10%
Total increase in commitment under accordion feature	$ 100.0
Maximum borrowing capacity	600.0	$ 500.0
Maximum borrowing capacity including accordion feature	$ 800.0	700.0
Leverage ratio, Covenant (as a percent)			60.00%
Leverage ratio (as a percent)			23.30%
Secured debt ratio, Covenant (as a percent)			40.00%
Secured debt ratio (as a percent)			0.00%
Fixed charge coverage ratio			8.0
Unhedged variable rate debt ratio, Covenant (as a percent)			30.00%
Unhedged variable rate debt ratio (as a percent)			12.30%
Credit Agreement \| Minimum
Debt
Fixed charge coverage ratio, Covenant			1.7
Credit Agreement \| Revolving Credit Facility
Debt
Maximum borrowing capacity		350.0
Credit Agreement \| Senior Unsecured Term Loan
Debt
Unsecured term loan		$ 150.0