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

No definition available.

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

- Definition

Represents the percentage of Senior Unsecured Term Notes that will have right to require our Operating Partnership to Purchase per the Note Purchase Agreement.

+ 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 percentage of Senior Unsecured Term Notes that holders may redeem for cash upon the occurrence of certain change of control events as defined in the Note Purchase Agreement.

+ 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 percentage of Senior Unsecured Term Notes that may be prepaid by the Operating Partnership per the Note Purchase Agreement.

+ References

No definition available.

+ Details

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Namespace Prefix:	cor_
Data Type:	num:percentItemType
Balance Type:	na
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, 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/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

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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=64930785&loc=d3e28551-108399

+ Details

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

- Definition

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

+ References

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ 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

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

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- Details

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Debt - Unsecured Debt (Details) - USD ($) $ in Thousands				3 Months Ended
Debt - Unsecured Debt (Details) - USD ($) $ in Thousands	Apr. 19, 2018	Feb. 02, 2016	Jun. 24, 2015	Mar. 31, 2018	Dec. 31, 2017	Apr. 20, 2017	Apr. 19, 2017	Jun. 15, 2016
Debt
Total principal outstanding				$ 991,500	$ 944,500
2020 Senior Unsecured Term Loan \| LIBOR \| Minimum \| Subsequent Event
Debt
Interest rate margin (as a percent)	1.40%
2020 Senior Unsecured Term Loan \| LIBOR \| Maximum \| Subsequent Event
Debt
Interest rate margin (as a percent)	2.00%
2020 Senior Unsecured Term Loan \| Base Rate \| Minimum \| Subsequent Event
Debt
Interest rate margin (as a percent)	0.40%
2020 Senior Unsecured Term Loan \| Base Rate \| Maximum \| Subsequent Event
Debt
Interest rate margin (as a percent)	1.00%
2020 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 150,000	$ 150,000
Debt Instrument, Interest Rate at Period End				3.16%	3.00%
2021 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 100,000	$ 100,000
Debt Instrument, Interest Rate at Period End				3.38%	3.06%
2022 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 200,000	$ 200,000
Debt Instrument, Interest Rate at Period End				3.28%	3.04%
2023 Senior Unsecured Term Loan \| Subsequent Event
Debt
Total principal outstanding	$ 150,000
Unsecured term loan	$ 150,000
Term of loan facility	5 years
2023 Senior Unsecured Term Loan \| LIBOR \| Minimum \| Subsequent Event
Debt
Interest rate margin (as a percent)	1.40%
2023 Senior Unsecured Term Loan \| LIBOR \| Maximum \| Subsequent Event
Debt
Interest rate margin (as a percent)	2.00%
2023 Senior Unsecured Term Loan \| Base Rate \| Minimum \| Subsequent Event
Debt
Interest rate margin (as a percent)	0.40%
2023 Senior Unsecured Term Loan \| Base Rate \| Maximum \| Subsequent Event
Debt
Interest rate margin (as a percent)	1.00%
2023 Senior Unsecured Term Loan \| Senior Unsecured Notes
Debt
Total principal outstanding				$ 150,000	$ 150,000
Debt Instrument, Interest Rate at Period End				4.19%	4.19%
2024 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 175,000	$ 175,000
Debt Instrument, Interest Rate at Period End				3.91%
Operating partnership \| LIBOR
Debt
Interest rate margin (as a percent)				1.55%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2020 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.20%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.50%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.20%
Operating partnership \| 2020 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Unsecured term loan		$ 150,000	$ 150,000
Term of loan facility			5 years
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2021 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.20%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.50%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.20%
Operating partnership \| 2021 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Unsecured term loan		$ 100,000
Term of loan facility		5 years
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR \| Minimum
Debt
Interest rate margin (as a percent)				1.50%
Operating partnership \| 2022 Senior Unsecured Term Loan \| LIBOR \| Maximum
Debt
Interest rate margin (as a percent)				2.10%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Base Rate \| Minimum
Debt
Interest rate margin (as a percent)				0.50%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Base Rate \| Maximum
Debt
Interest rate margin (as a percent)				1.10%
Operating partnership \| 2022 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Increase in accordion feature borrowing capacity							$ 300,000
Aggregate principal amount							$ 200,000
Operating partnership \| 2023 Senior Unsecured Term Loan \| Senior Unsecured Notes \| Private Placement
Debt
Aggregate principal amount								$ 150,000
Stated interest rate								4.19%
Percentage of term notes that may be prepaid								100.00%
Percentage of term notes that holders have right to purchase in cash								100.00%
Percentage of term notes that holders may redeem for cash								100.00%
Operating partnership \| 2024 Senior Unsecured Term Loan \| Senior Unsecured Term Loan
Debt
Unsecured term loan						$ 175,000
Stated interest rate						3.91%
Percentage of term notes that may be prepaid						100.00%
Percentage of term notes that holders have right to purchase in cash						100.00%
Percentage of term notes that holders may redeem for cash						100.00%