Deferred Costs (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred Costs [Abstract]
Deferred leasing	$ 385,555us-gaap_DeferredCostsLeasingGross	$ 326,379us-gaap_DeferredCostsLeasingGross
Deferred financing	193,776us-gaap_DeferredFinanceCostsGross	157,088us-gaap_DeferredFinanceCostsGross
Deferred costs, gross	579,331slg_DeferredCostsGross	483,467slg_DeferredCostsGross
Less accumulated amortization	(251,369)	(216,409)
Deferred costs, net	$ 327,962	$ 267,058

- Definition

For an unclassified balance sheet, this element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This amount is before considering accumulated amortization representing the periodic charge to earnings to recognize the deferred costs over the term of the related lease.

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