Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Amortization of acquired leases	$ 4.8	$ 34.8

Represents the increase (decrease) in rental revenue during the period resulting from the net amortization of acquired above-market and below-market leases.

No definition available.

Name:	slg_RentalRevenueIncreaseDecreaseAcquiredLeaseAmortization
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration