Significant Accounting Policies (Reclassification 2)(Details) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Debt Issuance Costs, Net	$ 82,300	$ 130,300
Limited partner interests in SLGOP	426,436	431,852
SL Green Operating Partnership
Error Corrections and Prior Period Adjustments Restatement [Line Items]
SL Green partner's capital	7,080,406	7,074,282
Partners' Capital	$ 7,750,911	$ 7,719,317	$ 7,459,216	$ 7,016,876
Common Stock | Partners' Interest | SL Green Operating Partnership
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' Capital Account, Units	100,562	99,976	97,325	94,993
Partners' Capital	$ 7,080,406	$ 7,074,282	$ 6,722,422	$ 6,318,684