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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Data Type:	num:percentItemType
Balance Type:	na
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- 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
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- Definition

Represents the leverage ratio as of the balance sheet date.

+ References

No definition available.

+ Details

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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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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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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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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

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
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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

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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

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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-SubTopic 210
-Section S99
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section S99
-Paragraph 1
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+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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://fasb.org/us-gaap/role/ref/legacyRef
-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

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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

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://fasb.org/us-gaap/role/ref/legacyRef
-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

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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Debt - Revolving Credit Facility (Details) $ in Thousands				9 Months Ended
Debt - Revolving Credit Facility (Details) $ in Thousands	Apr. 19, 2018 USD ($) item	Feb. 02, 2016 USD ($)	Jun. 24, 2015 USD ($)	Sep. 30, 2018 USD ($)	Apr. 18, 2018 USD ($)	Dec. 31, 2017 USD ($)	Apr. 19, 2017 USD ($)
Debt
Total principal outstanding				$ 1,079,500		$ 944,500
Revolving Credit Facility
Debt
Total principal outstanding				$ 154,500		169,500
Credit Agreement
Debt
Leverage ratio (as a percent)				24.80%
Secured debt ratio, Covenant (as a percent)				0.00%
Fixed charge coverage ratio				7.4
Credit Agreement \| Minimum
Debt
Fixed charge coverage ratio				1.50
Credit Agreement \| Maximum
Debt
Leverage ratio (as a percent)				0.60%
Secured debt ratio (as a percent)				0.40%
2023 Senior Unsecured Term Loan
Debt
Term of loan facility	5 years
Unsecured term loan	$ 150,000
2023 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)	1.40%
2023 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)	2.00%
2023 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)	0.40%
2023 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)	1.00%
2023 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 150,000
2020 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				150,000		150,000
2021 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				100,000		100,000
2022 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 200,000		$ 200,000
Operating partnership \| LIBOR
Debt
Interest rate margin (as a percent)				1.45%
Operating partnership \| 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	$ 250,000
Maximum borrowing capacity	850,000				$ 600,000
Maximum borrowing capacity including accordion feature	1,200,000
Borrowing capacity at end of period				$ 450,000
Letters of credit outstanding				4,900
Amount available for borrowing under the facility				$ 290,600
Operating partnership \| Credit Agreement \| Revolving Credit Facility
Debt
Maximum borrowing capacity	450,000				$ 350,000
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.45%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.05%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.45%
Operating partnership \| Credit Agreement \| Revolving Credit Facility \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.05%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Term of loan facility			5 years
Unsecured term loan	$ 150,000		$ 150,000
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Term of loan facility		5 years
Unsecured term loan		$ 100,000
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Increase in accordion feature borrowing capacity							$ 300,000