Partners' Capital of the Operating Partnership (Details)	Sep. 30, 2015 unit shares	Dec. 31, 2014 unit shares
Common Stock
Stockholders' Equity
Units outstanding (units)	99,659,000	97,325,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	3.74%	3.92%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units) | unit	3,874,750	3,973,016
SL Green Operating Partnership | Series I Preferred Units
Stockholders' Equity
Units outstanding (units)	9,200,000
SL Green Operating Partnership | Common Stock
Stockholders' Equity
Units outstanding (units)	99,659,376