Significant Accounting Policies - Deferred Lease Costs (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Portion of compensation capitalized	$ 8.5	$ 6.8	$ 6.6
Estimated average lease term (in years)	7 years

Represents the amount of deferred lease costs capitalized during the period.

No definition available.

Name:	slg_DeferredLeaseCostsCapitalizedInPeriod
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration