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Represents the duration of each offering period during which the shares are offered for purchase under the stock-based compensation plan of the entity.

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Represents the approximate amount of awards that may be earned by the recipients of the plan any time after the beginning of the second year, if the maximum performance has been achieved.

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Represents the approximate amount of awards that may be earned by the recipients of the plan any time after the beginning of the third year, if the maximum performance has been achieved.

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Represents the awards earned by all participants under the stock based compensation plans.

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Represents the amount of the maximum dilution cap on the value of awards that could be earned under stock based compensation plans.

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Represents the percentage of value of the award amortized over the period of five years from the date of grant.

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Represents the percentage of stock price appreciation at which the minimum approximate amount of awards will be earned by recipients of the stock-based compensation plan.

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Represents the threshold percentage of return to be achieved by the holders of the entity's common equity, above which awards may be granted to plan participants.

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Represents the period for appreciation of the stock price of the entity to be taken into consideration for arriving at the amount of awards to be granted under the stock-based compensation plan.

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Represents the period over which the remainder of the award vests based on continued employment with the company.

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Represents the price at which the employees can purchase the shares of common stock of the entity under stock-based compensation plans. Such price is expressed as a percentage of lesser of market value of the shares on the first day or the last day of the offering period under that plan.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

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Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

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Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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Equity-based compensation cost during the period with respect to the award, which will be recognized in income (as well as the total recognized tax benefit) or capitalized as part of the cost of an asset.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Equity (Details 4) (USD $)	1 Months Ended	6 Months Ended			1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended		6 Months Ended
Equity (Details 4) (USD $)	Apr. 30, 2007 2003 Long-Term Outperformance Compensation Program	Jun. 30, 2011 2003 Long-Term Outperformance Compensation Program	Jun. 30, 2010 2003 Long-Term Outperformance Compensation Program	Mar. 31, 2007 2003 Long-Term Outperformance Compensation Program	Nov. 30, 2008 2005 Long-Term Outperformance Compensation Program	Jun. 30, 2010 2005 Long-Term Outperformance Compensation Program	Jun. 30, 2011 2005 Long-Term Outperformance Compensation Program	Jun. 30, 2010 2005 Long-Term Outperformance Compensation Program	Dec. 31, 2010 2005 Long-Term Outperformance Compensation Program	Jun. 14, 2006 2005 Long-Term Outperformance Compensation Program	Jun. 08, 2006 2005 Long-Term Outperformance Compensation Program	Jun. 30, 2011 2006 Long-Term Outperformance Compensation Program	Jun. 30, 2010 2006 Long-Term Outperformance Compensation Program	Jun. 30, 2011 2006 Long-Term Outperformance Compensation Program	Jun. 30, 2010 2006 Long-Term Outperformance Compensation Program	Jun. 30, 2011 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Jun. 30, 2010 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Jun. 30, 2011 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Jun. 30, 2010 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Dec. 31, 2009 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Jan. 31, 2011 SL Green Realty Corp. 2010 Notional Unit Long-Term Compensation Plan	Jun. 30, 2011 Deferred Stock Compensation Plan for Directors	Jun. 30, 2011 Employee Stock Purchase Plan	Jan. 31, 2008 Employee Stock Purchase Plan
Stock based compensation
Term of long-term compensation program (in years)		7
Minimum return to be achieved for restricted stock awards to be made to plan participants (as a percent)		40.00%					30.00%
Performance period		48 months					three years
Maximum performance pool established, net of forfeitures	$ 22,825,000									$ 49,250,000
Awards granted (in shares)	166,312																			744,128		7,765
Percentage of each award vested (as a percent)				40.00%
Number of years over which remaining percentage of each award is vested (in years)				3			2
Fair value of awards on grant date		3,200,000
Percentage of value of awards amortized over four years (as a percent)		40.00%
Percentage of value of awards amortized over five years (as a percent)		20.00%
Percentage of value of awards amortized per year for five years (as a percent)		20.00%
Percentage of value of awards amortized over six years (as a percent)		20.00%
Percentage of value of awards amortized per year for six years (as a percent)		16.67%
Percentage of value of awards amortized over seven years (as a percent)		20.00%
Percentage of value of awards amortized per year for seven years (as a percent)		14.29%
Compensation expense			23,000			1,200,000		1,600,000				30,000	100,000	60,000	100,000	2,200,000	1,100,000	4,200,000	1,600,000
Number of consecutive days of maximum performance to earn awards earlier (in days)							30
Value of LTIP Units that could be earned expressed as percentage of outperformance amount in excess of the 30% benchmark (as a percent)							10.00%
Maximum dilution cap as percentage of outstanding shares and units of limited partnership interest (as a percent)							3.00%
Maximum dilution cap							50,000,000
LTIP units earned (in shares)											490,475										366,815
Portion of earned LTIP Units vested					one-third
Cost of the plan, subject to adjustment for forfeitures									8,000,000					16,400,000					31,500,000
Approximate amount of LTIP units that may be earned by the recipients based on stock price appreciation, minimum																15,000,000		15,000,000
Approximate amount of LTIP units that may be earned by the recipients based on stock price appreciation, maximum																75,000,000		75,000,000
Period for appreciation of stock price (in years)																3		3
Approximate amount of awards that may be earned by recipients after beginning of the second year if maximum performance achieved																25,000,000		25,000,000
Approximate amount of awards that may be earned by recipients after beginning of the third year if maximum performance achieved																25,000,000		25,000,000
Stock price appreciation to earn minimum amount of awards (as a percent)																25.00%		25.00%
Minimum stock price appreciation to earn maximum amount of awards (as a percent)																$ 50.00%		$ 50.00%
Percentage of aggregate stock price appreciation below which no awards will be earned (as a percent)																25.00%		25.00%
Percentage of LTIP Units earned, vesting on January 1, 2013 (as a percent)																50.00%		50.00%
Percentage of LTIP Units earned, vesting on January 1, 2014 (as a percent)																25.00%		25.00%
Percentage of LTIP Units earned, vesting on January 1, 2015 (as a percent)																25.00%		25.00%
Period over which remainder of awards is scheduled to vest ratably (in years)																		2
Maximum potential awards of LTIP units (in shares)																1,179,987		1,179,987
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (as a percent)																						100.00%
Phantom stock units outstanding (in shares)																						66,431
Shares of common stock available for issuance (in shares)																								500,000
Duration of each offering period (in months)																							3
Purchase price as a percentage of market value of the common stock (as a percent)																							85.00%
Shares of common stock issued (in shares)																							51,929