Noncontrolling Interests on the Company's Consolidated Financial Statements (Common Unit Activity) (Details) - SL Green Operating Partnership - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Rollforward Analysis of Preferred Unit Activity
Issuance of units	$ 18,140	$ 30,506
Redemption of units	(7,152)	(55,697)
Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	282,516	71,115
Issuance of units	22,793	211,601
Redemption of units	(440)	(200)
Balance at end of period	$ 304,869	$ 282,516

Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=51664549&loc=SL4569655-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=51664549&loc=SL4616395-111683

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Period Type:	duration