Rental Income - Future Minimum Rents (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Lessor, Lease, Description [Line Items]
Total payments to be received	$ 1,700,000
Consolidated properties
Lessor, Lease, Description [Line Items]
Remaining 2019	429,598
2020	806,444
2021	664,107
2022	602,660
2023	537,219
2024	495,359
Thereafter	3,095,390
Total payments to be received	6,630,777
Unconsolidated properties
Lessor, Lease, Description [Line Items]
Remaining 2019	173,809
2020	373,884
2021	381,155
2022	364,189
2023	337,150
2024	309,479
Thereafter	1,840,974
Total payments to be received	$ 3,780,640

Lessor, Operating Lease, Payments To Be Received, After Six Years

No definition available.

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- Definition

Lessor, Operating Lease, Payments To Be Received, Six Years

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
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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

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Namespace Prefix:	us-gaap_
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- Definition

Amount of lease payments to be received by lessor for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77888428&loc=SL77919396-209981

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in fifth fiscal year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest statement of financial position date.

+ References

+ Details

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- Definition

Amount of lease payments to be received by lessor in fourth year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

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

- Definition

Amount of lease payments to be received by lessor in remainder of fiscal year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77888428&loc=SL77919396-209981

+ Details

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- Definition

Amount of lease payments to be received by lessor in third fiscal year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

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Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in second fiscal year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

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