Consolidated Statement of Capital - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest						$ (20,650)
Conversion of common units					$ 31,806	55,697	$ 31,653
DRSPP proceeds					277	99,555	64
Reallocation of capital account relating to sale						(10,143)
Reallocation of noncontrolling interests in the operating partnership					4,222	20,915	168,439
Deferred compensation plan and stock award, net					(1,988)	(2,982)	(1,514)
Amortization of deferred compensation plan					25,890	26,721	$ 29,749
Contributions - net proceeds from common stock offering (in units)							1,626,999
Cash distributions to noncontrolling interests					(15,419)	(119,784)	$ (7,019)
Common Stock
Increase (Decrease) in Partner's Capital
Conversion of common units					$ 3	$ 5	$ 3
DRSPP (in units)					2,000	776,000
DRSPP proceeds						$ 8
Deferred compensation plan and stock award, net, as adjusted (in units)					96,000	168,000	15,000
Deferred compensation plan and stock award, net					$ 1	$ 2
Contributions - net proceeds from common stock offering (in units)						1,007,000	1,654,000
Contributions - proceeds from stock options exercised (in units)					193,000	217,000	348,000
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest						$ (11,084)
Reallocation of capital account relating to sale						(10,143)
Cash distributions to noncontrolling interests					$ (15,419)	(119,784)	$ (7,019)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 7,719,317		$ 7,459,216	7,719,317	7,459,216	7,016,876
Net income					257,540	299,927	524,646
Acquisition of subsidiary interest from noncontrolling interest						(20,650)
Other comprehensive (loss)					30,886	(1,769)	8,231
Preferred distributions	$ (4,252)	(4,622)	$ (5,277)	(6,878)	(14,950)	(14,952)	(14,952)
Conversion of common units					31,806	55,697	31,653
DRSPP proceeds					277	99,555	64
Reallocation of capital account relating to sale						(10,143)
Reallocation of noncontrolling interests in the operating partnership					4,222	20,915	168,439
Deferred compensation plan and stock award, net					(1,988)	(2,982)	(1,514)
Amortization of deferred compensation plan					25,890	26,721	29,749
Issuance of stock					(40)
Contribution to consolidated joint venture interests					2,359	35,178	30,800
Contributions - net proceeds from common stock offering						126,989	185,321
Contributions - proceeds from stock options exercised					14,832	16,362	25,211
Cash distributions to noncontrolling interests					(15,419)	(119,784)	(7,019)
Cash distributions declared ($2.52, $2.10, and $1.49 per common unit, respectively, none of which represented a return of capital for federal income tax purposes)					(295,377)	(250,963)	(201,411)
Ending Balance	7,750,911		7,719,317		7,750,911	7,719,317	7,459,216
SL Green Operating Partnership | Preferred Units | Series C Preferred Stock
Increase (Decrease) in Partner's Capital
Beginning Balance		0		0	0	0	0
Ending Balance	0		0		0	0	0
SL Green Operating Partnership | Preferred Units | Series I Preferred Stock
Increase (Decrease) in Partner's Capital
Beginning Balance		221,932		221,932	221,932	221,932	221,932
Ending Balance	221,932		221,932		221,932	221,932	221,932
SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 7,074,282		$ 6,722,422	$ 7,074,282	$ 6,722,422	$ 6,318,684
Beginning Balance (units)		99,976,000		97,325,000	99,976,000	97,325,000	94,993,000
Net income					$ 249,896	$ 284,084	$ 518,056
Acquisition of subsidiary interest from noncontrolling interest						(9,566)
Preferred distributions					$ (14,950)	$ (14,952)	$ (14,952)
Conversion of common units (in units)					295,000	483,000	315,000
Conversion of common units					$ 31,806	$ 55,697	$ 31,653
DRSPP (in units)						776,000
DRSPP proceeds					277	$ 99,555	64
Reallocation of noncontrolling interests in the operating partnership					$ 4,222	$ 20,915	$ 168,439
Deferred compensation plan and stock award, net, as adjusted (in units)					96,000	168,000	15,000
Deferred compensation plan and stock award, net					$ (1,988)	$ (2,982)	$ (1,514)
Amortization of deferred compensation plan					25,890	$ 26,721	$ 29,749
Issuance of stock					$ (40)
Contributions - net proceeds from common stock offering (in units)						1,007,000	1,654,000
Contributions - net proceeds from common stock offering						$ 126,989	$ 185,321
Contributions - proceeds from stock options exercised (in units)					193,000	217,000	348,000
Contributions - proceeds from stock options exercised					$ 14,832	$ 16,362	$ 25,211
Cash distributions declared ($2.52, $2.10, and $1.49 per common unit, respectively, none of which represented a return of capital for federal income tax purposes)					(295,377)	(250,963)	(201,411)
Ending Balance	$ 7,080,406		$ 7,074,282		$ 7,080,406	$ 7,074,282	$ 6,722,422
Ending Balance (units)	100,562,000		99,976,000		100,562,000	99,976,000	97,325,000
SL Green Operating Partnership | Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partner's Capital
Beginning Balance		$ (8,749)		$ (6,980)	$ (8,749)	$ (6,980)	$ (15,211)
Other comprehensive (loss)					30,886	(1,769)	8,231
Ending Balance	$ 22,137		$ (8,749)		22,137	(8,749)	(6,980)
SL Green Operating Partnership | Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 431,852		$ 521,842	431,852	521,842	491,471
Net income					7,644	15,843	6,590
Acquisition of subsidiary interest from noncontrolling interest						(11,084)
Reallocation of capital account relating to sale						(10,143)
Contribution to consolidated joint venture interests					2,359	35,178	30,800
Cash distributions to noncontrolling interests					(15,419)	(119,784)	(7,019)
Ending Balance	$ 426,436		$ 431,852		$ 426,436	$ 431,852	$ 521,842