Partners' Capital of the Operating Partnership - Additional Information (Details)	3 Months Ended
Mar. 31, 2018 shares	Dec. 31, 2017 shares
Common Stock
Stockholders' Equity
Units outstanding (units)	89,135,000	92,803,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	5.02%	4.58%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units)	4,715,338	4,452,979
SL Green Operating Partnership \| Series I Preferred Units
Stockholders' Equity
Units outstanding (units)	9,200,000
Period of restriction to redeem OP Units	1 year
Conversion of stock, shares issued	1
SL Green Operating Partnership \| Common Stock
Stockholders' Equity
Units outstanding (units)	89,135,009

The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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