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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- Definition

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

+ References

No definition available.

+ Details

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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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Namespace Prefix:	cor_
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- Definition

Represents the leverage 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 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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Period Type:	duration

- 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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Namespace Prefix:	cor_
Data Type:	num:percentItemType
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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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Data Type:	num:percentItemType
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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

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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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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Data Type:	num:percentItemType
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- 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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

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

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-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-02.22)

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-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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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

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Data Type:	xbrli:stringItemType
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- 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 45

-Paragraph 2

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

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-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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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

Reference 1: 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

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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-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

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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- 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

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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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

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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)

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-Number 210

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-Name Accounting Standards Codification

-Topic 944

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- 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

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))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Details

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Debt (Details) (USD $)	0 Months Ended	3 Months Ended	0 Months Ended
Debt (Details) (USD $)	Apr. 09, 2015	Mar. 31, 2015 item	Jan. 31, 2014	Feb. 03, 2014	Feb. 03, 2014	Dec. 31, 2014
Debt
Total principal outstanding		$ 333,750,000us-gaap_DebtInstrumentCarryingAmount				$ 318,500,000us-gaap_DebtInstrumentCarryingAmount
Revolving credit facility		233,750,000us-gaap_LineOfCredit				218,500,000us-gaap_LineOfCredit
LIBOR
Debt
Reference rate	one-month LIBOR
Revolving Credit Facility
Debt
Interest rate as of reporting date (as a percent)		2.18%				2.17%
Total principal outstanding		233,750,000				218,500,000
Commitment under the credit agreement		405,000,000
Number of options available for extensions		1
Extension fee (as a percent)		0.25%
Amount available for borrowing under the facility		163,900,000
Revolving credit facility		233,800,000
Letters of credit		7,300,000
Leverage ratio (as a percent)		17.10%
Secured debt ratio (as a percent)		0.00%
Unhedged variable rate debt ratio (as a percent)		11.80%
Revolving Credit Facility \| Operating partnership
Debt
Commitment under the credit agreement		500,000,000
Revolving Credit Facility \| Minimum
Debt
Fixed charge coverage ratio, Covenant		1.75
Fixed charge coverage ratio		8.80%
Revolving Credit Facility \| Maximum
Debt
Leverage ratio (as a percent)		60.00%
Secured debt ratio, Covenant (as a percent)		40.00%
Secured debt ratio (as a percent)		40.00%
Unhedged variable rate debt ratio (as a percent)		30.00%
Revolving Credit Facility \| LIBOR \| Operating partnership
Debt
Reference rate		LIBOR
Interest rate margin (as a percent)		2.00%
Leverage ratio (as a percent)		17.10%
Revolving Credit Facility \| LIBOR \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)		2.00%
Revolving Credit Facility \| LIBOR \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		2.75%
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)		1.00%
Revolving Credit Facility \| Base rate \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)		1.75%
Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)		3.23%
Total principal outstanding		100,000,000				100,000,000
Commitment under the credit agreement			100,000,000
Term of loan facility			5 years
Amount available for borrowing under the facility			100,000,000
Senior Unsecured Term Loan \| Interest Rate Swap
Debt
Interest rate margin (as a percent)				3.23%
Notional amount of interest rate derivatives				100,000,000	100,000,000
Amount borrowed under term loan or revolving credit facility				100,000,000	100,000,000
Term of derivative				5 years
Senior Unsecured Term Loan \| Operating partnership
Debt
Commitment under the credit agreement			200,000,000
Total increase in commitment under accordion feature			$ 100,000,000
Senior Unsecured Term Loan \| LIBOR \| Interest Rate Swap
Debt
Reference rate					one-month LIBOR
Senior Unsecured Term Loan \| LIBOR \| Operating partnership
Debt
Reference rate		LIBOR	LIBOR
Interest rate margin (as a percent)		1.75%
Leverage ratio (as a percent)		17.10%
Senior Unsecured Term Loan \| LIBOR \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)			1.75%
Senior Unsecured Term Loan \| LIBOR \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)			2.65%
Senior Unsecured Term Loan \| Base rate \| Operating partnership
Debt
Reference rate			base rate
Senior Unsecured Term Loan \| Base rate \| Minimum \| Operating partnership
Debt
Interest rate margin (as a percent)			0.75%
Senior Unsecured Term Loan \| Base rate \| Maximum \| Operating partnership
Debt
Interest rate margin (as a percent)			1.65%