Capital (Details 2) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Third Amended and Restated 2005 Stock Option and Incentive Plan
Third amended and restated 2005 stock option and incentive plan
Fungible units available for issuance (in shares)	5,800,000		5,800,000
SL Green | Full-value awards
Third amended and restated 2005 stock option and incentive plan
Fungible units per share	2.76		2.76
SL Green | Stock options, stock appreciation rights and other awards
Third amended and restated 2005 stock option and incentive plan
Award expiration period			5 years
SL Green | Stock options, stock appreciation rights and other awards | Granted on or after June 13, 2013
Third amended and restated 2005 stock option and incentive plan
Fungible units per share	0.77		0.77
SL Green | All other awards
Third amended and restated 2005 stock option and incentive plan
Fungible units per share	1.0		1.0
SL Green | Stock options
Third amended and restated 2005 stock option and incentive plan
Award expiration period			10 years
Weighted average assumptions used for estimation of fair value of each stock option
Dividend yield (as a percent)			2.00%		2.00%
Expected life of option			4 years 8 months 12 days		3 years 8 months 12 days
Risk-free interest rate (as a percent)			0.68%		0.46%
Expected stock price volatility (as a percent)			35.50%		37.40%
Options Outstanding
Balance at beginning of year (in shares)			1,201,000	1,277,200	1,277,200
Granted (in shares)			201,000		361,331
Exercised (in shares)			(156,730)		(382,612)
Lapsed or cancelled (in shares)			(24,035)		(54,919)
Balance at end of year (in shares)	1,221,235		1,221,235		1,201,000
Options exercisable at end of year (in shares)	504,092		504,092		479,913
Weighted average fair value of awards granted during the year			$ 3,867,342		$ 6,602,967
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)			$ 75.05	$ 63.37	$ 63.37
Granted (in dollars per share)			$ 76.67		$ 75.36
Exercised (in dollars per share)			$ 51.89		$ 36.65
Lapsed or cancelled (in dollars per share)			$ 84.71		$ 72.99
Balance at end of year (in dollars per share)	$ 78.10		$ 78.10		$ 75.05
Options exercisable at end of year (in dollars per share)	$ 85.05		$ 85.05		$ 86.85
Exercise price of options granted, low end of the range (in dollars per share)			$ 20.67
Exercise price of options granted, high end of the range (in dollars per share)			$ 137.18
Remaining weighted average contractual life of the options outstanding			4 years 3 months 25 days
Remaining weighted average contractual life of the options exercisable			3 years 7 months 20 days
Share-based compensation, additional disclosures
Compensation expense	1,300,000	1,100,000	2,600,000	2,800,000
Total unrecognized compensation cost related to unvested stock awards	10,100,000		10,100,000
Weighted average period for recognition of compensation cost related to unvested stock awards			3 years
SL Green | Stock options | Minimum
Third amended and restated 2005 stock option and incentive plan
Options vesting period, maximum			1 year
SL Green | Stock options | Maximum
Third amended and restated 2005 stock option and incentive plan
Options vesting period, maximum			5 years
SL Green | Restricted Stock Awards
Options Outstanding
Weighted average fair value of awards granted during the year			309,362		7,023,942
Share-based compensation, additional disclosures
Compensation expense			2,971,339		6,930,381
Total unrecognized compensation cost related to unvested stock awards	9,500,000		9,500,000
Weighted average period for recognition of compensation cost related to unvested stock awards			2 years 1 month 6 days
Annual award vesting rate, low end of the range (as a percent)			15.00%
Annual award vesting rate, high end of the range (as a percent)			35.00%
Summary of restricted stock
Balance at beginning of year (in shares)			2,804,901	2,912,456	2,912,456
Granted (in shares)			3,450		92,729
Cancelled (in shares)			(600)		(200,284)
Balance at end of year (in shares)	2,807,751		2,807,751		2,804,901
Vested during the year (in shares)			500		408,800
Fair value of restricted stock vested during the year			20,000		22,400,000
Compensation expense related to long-term compensation plans, restricted stock and stock options capitalized to assets	$ 1,000,000	$ 1,000,000	$ 2,000,000	$ 2,000,000
SL Green | Third Amended and Restated 2005 Stock Option and Incentive Plan
Third amended and restated 2005 stock option and incentive plan
Maximum fungible units that may be granted (in shares)	17,130,000		17,130,000
Shares that may be issued if equal to fungible units	17,130,000		17,130,000