Consolidated Balance Sheets (USD $)	Sep. 30, 2013	Dec. 31, 2012
Commercial real estate properties, at cost:
Land and land interests	$ 2,868,833,000	$ 2,886,099,000
Building and improvements	7,440,543,000	7,389,766,000
Building leasehold and improvements	1,353,997,000	1,346,748,000
Properties under capital lease	50,332,000	40,340,000
Total commercial real estate properties, at cost	11,713,705,000	11,662,953,000
Less: accumulated depreciation	(1,574,002,000)	(1,393,323,000)
Total commercial real estate properties, net	10,139,703,000	10,269,630,000
Assets held for sale	0	4,901,000
Cash and cash equivalents	209,098,000	189,984,000
Restricted cash	356,844,000	136,071,000
Investment in marketable securities	32,863,000	21,429,000
Tenant and other receivables, net of allowance of $22,383 and $21,652 in 2013 and 2012, respectively	51,354,000	48,544,000
Related party receivables	7,800,000	7,531,000
Deferred rents receivable, net of allowance of $29,508 and $29,580 in 2013 and 2012, respectively	374,615,000	340,747,000
Debt and preferred equity investments, net of discounts and deferred origination fees of $26,466 and $22,341 in 2013 and 2012, and allowance of $4,000 and $7,000 in 2013 and 2012, respectively	1,315,551,000	1,348,434,000
Investments in unconsolidated joint ventures	1,109,815,000	1,032,243,000
Deferred costs, net	247,850,000	261,145,000
Other assets	729,426,000	718,326,000
Total assets	14,574,919,000	14,378,985,000
Liabilities
Mortgages and other loans payable	4,641,758,000	4,615,464,000
Revolving credit facility	340,000,000	70,000,000
Term loan and senior unsecured notes	1,737,869,000	1,734,956,000
Accrued interest payable and other liabilities	69,359,000	73,769,000
Accounts payable and accrued expenses	167,719,000	159,598,000
Deferred revenue	293,393,000	312,995,000
Capitalized lease obligations	47,492,000	37,518,000
Deferred land leases payable	21,066,000	20,897,000
Dividend and distributions payable	34,749,000	37,839,000
Security deposits	54,824,000	46,253,000
Liabilities related to assets held for sale	0	136,000
Junior subordinate deferrable interest debentures held by trusts that issued trust preferred securities	100,000,000	100,000,000
Total liabilities	7,508,229,000	7,209,425,000
Commitments and contingencies	0	0
Balance at the beginning of period	248,046,000	212,907,000
Equity
Common stock, $0.01 par value, 160,000 shares authorized and 95,780 and 94,896 issued and outstanding at September 30, 2013 and December 31, 2012, respectively (including 3,566 and 3,646 shares held in Treasury at September 30, 2013 and December 31, 2012, respectively)	959,000	950,000
Additional paid-in-capital	4,757,778,000	4,667,900,000
Treasury stock at cost	(316,989,000)	(322,858,000)
Accumulated other comprehensive loss	(19,249,000)	(29,587,000)
Retained earnings	1,636,584,000	1,701,092,000
Total SL Green stockholders' equity	6,281,015,000	6,419,802,000
Noncontrolling interests in other partnerships	488,079,000	487,301,000
Total equity	6,769,094,000	6,907,103,000
Total liabilities and equity	14,574,919,000	14,378,985,000
Series G Preferred Units
Liabilities
Preferred Units	47,550,000	47,550,000
Series H Preferred Units
Liabilities
Preferred Units	2,000,000	2,000,000
Series C Preferred Units
Equity
Preferred stock	0	180,340,000
Series I Preferred Units
Equity
Preferred stock	221,932,000	221,965,000
SL Green Operating Partnership
Commercial real estate properties, at cost:
Land and land interests	2,868,833,000	2,886,099,000
Building and improvements	7,440,543,000	7,389,766,000
Building leasehold and improvements	1,353,997,000	1,346,748,000
Properties under capital lease	50,332,000	40,340,000
Total commercial real estate properties, at cost	11,713,705,000	11,662,953,000
Less: accumulated depreciation	(1,574,002,000)	(1,393,323,000)
Total commercial real estate properties, net	10,139,703,000	10,269,630,000
Assets held for sale	0	4,901,000
Cash and cash equivalents	209,098,000	189,984,000
Restricted cash	356,844,000	136,071,000
Investment in marketable securities	32,863,000	21,429,000
Tenant and other receivables, net of allowance of $22,383 and $21,652 in 2013 and 2012, respectively	51,354,000	48,544,000
Related party receivables	7,800,000	7,531,000
Deferred rents receivable, net of allowance of $29,508 and $29,580 in 2013 and 2012, respectively	374,615,000	340,747,000
Debt and preferred equity investments, net of discounts and deferred origination fees of $26,466 and $22,341 in 2013 and 2012, and allowance of $4,000 and $7,000 in 2013 and 2012, respectively	1,315,551,000	1,348,434,000
Investments in unconsolidated joint ventures	1,109,815,000	1,032,243,000
Deferred costs, net	247,850,000	261,145,000
Other assets	729,426,000	718,326,000
Total assets	14,574,919,000	14,378,985,000
Liabilities
Mortgages and other loans payable	4,641,758,000	4,615,464,000
Revolving credit facility	340,000,000	70,000,000
Term loan and senior unsecured notes	1,737,869,000	1,734,956,000
Accrued interest payable and other liabilities	69,359,000	73,769,000
Accounts payable and accrued expenses	167,719,000	159,598,000
Deferred revenue	293,393,000	312,995,000
Capitalized lease obligations	47,492,000	37,518,000
Deferred land leases payable	21,066,000	20,897,000
Dividend and distributions payable	34,749,000	37,839,000
Security deposits	54,824,000	46,253,000
Liabilities related to assets held for sale	0	136,000
Junior subordinate deferrable interest debentures held by trusts that issued trust preferred securities	100,000,000	100,000,000
Total liabilities	7,508,229,000	7,209,425,000
Commitments and contingencies	0	0
Equity
Accumulated other comprehensive loss	(19,821,000)	(30,649,000)
Total liabilities and equity	14,574,919,000	14,378,985,000
SLGOP Partners' Capital
General And Limited Partners Capital Account	6,259,229,000	6,189,529,000
Limited Partners' Capital Account	67,721,000	71,524,000
Partners' Capital	6,529,061,000	6,632,709,000
Partners' Capital Attributable to Noncontrolling Interest	488,079,000	487,301,000
Total capital	7,017,140,000	7,120,010,000
SL Green Operating Partnership | Series G Preferred Units
Liabilities
Preferred Units	47,550,000	47,550,000
SL Green Operating Partnership | Series H Preferred Units
Liabilities
Preferred Units	2,000,000	2,000,000
SL Green Operating Partnership | Series C Preferred Units
SLGOP Partners' Capital
Preferred Units, Preferred Partners' Capital Accounts	0	180,340,000
Total capital	0	180,340,000
SL Green Operating Partnership | Series I Preferred Units
SLGOP Partners' Capital
Preferred Units, Preferred Partners' Capital Accounts	221,932,000	221,965,000
Total capital	$ 221,932,000	$ 221,965,000