Debt Instrument, Increase (Decrease) in Basis Spread on Variable Rate

No definition available.

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- Definition

Debt Instrument, Increase (Decrease) in Facility Fee

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Debt Origination and Legal Costs

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line of Credit Facility, Increase (Decrease) in Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The expanded maximum borrowing capacity available, which is subject to agreement with the entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of years from the issuance of debt for which the fixed rate of interest will be in force.

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: 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(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: 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(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentLineItems
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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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: 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

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- 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))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ 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

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_RevolvingCreditFacilityMember
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Corporate Indebtedness (Details) (USD $)	12 Months Ended	1 Months Ended			12 Months Ended	1 Months Ended
Corporate Indebtedness (Details) (USD $)	Dec. 31, 2014	Nov. 30, 2014	Mar. 31, 2014	Jan. 31, 2015	Dec. 31, 2013	Jun. 30, 2005	Nov. 30, 2012
Corporate Indebtedness
Credit facility, maximum borrowing capacity							$ 1,600,000,000.0
Outstanding under line of credit facility	385,000,000us-gaap_LineOfCredit				220,000,000us-gaap_LineOfCredit
2012 Credit Facility
Corporate Indebtedness
Letters of credit	113,200,000
Ability to borrow under line of credit facility	701,800,000
Debt origination	3,000,000
Revolving credit facility
Corporate Indebtedness
Credit facility, maximum borrowing capacity							1,200,000,000.0
Maximum borrowing capacity, optional expansion							1,500,000,000.0
Effective rate (as a percent)	1.61%
Outstanding under line of credit facility	385,000,000
Revolving credit facility \| Maximum
Corporate Indebtedness
Unused balance fee	0.35%
Revolving credit facility \| Minimum
Corporate Indebtedness
Facility fee	0.30%
Unused balance fee	0.15%
Revolving credit facility \| LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.45%
Revolving credit facility \| LIBOR \| Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.75%
Revolving credit facility \| LIBOR \| Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.00%
Term loan
Corporate Indebtedness
Credit facility, maximum borrowing capacity	833,000,000	833,000,000	783,000,000
Increase in credit facility		50,000,000	383,000,000
Decrease in basis points			0.25%
Effective rate (as a percent)	1.67%
Term loan \| LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.40%
Term loan \| LIBOR \| Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.90%
Term loan \| LIBOR \| Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	0.95%
Term loan \| Subsequent Event
Corporate Indebtedness
Decrease in basis points				0.20%
Facility fee				0.05%
2011 Revolving Credit Facility
Corporate Indebtedness
Credit facility, maximum borrowing capacity	1,500,000,000
2011 Revolving Credit Facility \| Maximum
Corporate Indebtedness
Unused balance fee					0.45%
2011 Revolving Credit Facility \| Minimum
Corporate Indebtedness
Unused balance fee					0.175%
2011 Revolving Credit Facility \| LIBOR \| Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)					1.85%
2011 Revolving Credit Facility \| LIBOR \| Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)					1.00%
Trust Preferred Securities
Corporate Indebtedness
Debt instrument issued, value						$ 100,000,000
Interest rate (as a percent)	5.61%
Number of years for which securities will bear fixed rate of interest						10 years
Trust Preferred Securities \| LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.25%