Debt Instrument, Number of Extension Options

No definition available.

Name:	slg_DebtInstrumentNumberofExtensionOptions
Namespace Prefix:	slg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Period of Extension Option

+ References

No definition available.

+ Details

Name:	slg_DebtInstrumentPeriodofExtensionOption
Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Basis Point Fee

+ References

No definition available.

+ Details

Name:	slg_LineofCreditFacilityBasisPointFee
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Threshold Amount for Basis Point Fee

+ References

No definition available.

+ Details

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

- Definition

Secured Debt, Amount Transferred to Liabilities Related to Net Assets Held for Sale

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtAmountTransferredtoLiabilitiesRelatedtoNetAssetsHeldforSale
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations and other loans payable.

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtAndOtherLoansPayable
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the carrying amount of long-term secured loans outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtBearingFixedInterestAmount
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Secured Debt, Bearing Fixed Interest, Mortgage Amount

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtBearingFixedInterestMortgageAmount
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Secured Debt, Bearing Fixed Interest, Subordinate Loan Amount

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtBearingFixedInterestSubordinateLoanAmount
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the carrying amount of long-term secured loans outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtBearingVariableInterestAmount
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Secured Debt, Deferred Finance Costs, Net

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtDeferredFinanceCostsNet
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Secured Debt, Gross

+ References

No definition available.

+ Details

Name:	slg_SecuredDebtGross
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624258-113959

+ Details

Name:	us-gaap_CollateralAlreadyPostedAggregateFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtPercentageBearingFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtPercentageBearingVariableInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph (12)(c)
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph (16)(c)
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph 15
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph 14
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

+ Details

Name:	us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The per share liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.28(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_TemporaryEquityLiquidationPreferencePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_StatementClassOfStockAxis=slg_SeriesJPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=slg_FHLBAdvanceMaturinginJanuary2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=slg_FHLBAdvanceMaturinginJanuary20172Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=slg_UncommittedMasterRepurchaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_LandmarkSquareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_LexingtonAvenue485Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_MadisonAvenue762Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_OneMadisonAvenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_ChurchStreet100Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_ThirdAvenue919Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_East400Street58Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_LexingtonAvenue420Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_Broadway1515Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_ThirdAvenue885Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_SevenOneNineSeventhAvenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_A187Broadwayand57DeyStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_Amsterdam1080Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_A315West33rdStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_East220Street42Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_OneVanderbiltMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=slg_AmsterdamAvenue1080Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_SeniorSubordinatedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Mortgages and Other Loans Payable (Details)		1 Months Ended	3 Months Ended
Mortgages and Other Loans Payable (Details)	Dec. 06, 2015 USD ($)	Sep. 30, 2016 USD ($) extenstion_option	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Total fixed rate debt			$ 3,579,382,000	$ 3,518,127,000
Total floating rate debt			657,163,000	622,585,000
Total fixed rate and floating rate debt			4,236,545,000	4,140,712,000
Mortgages reclassed to liabilities related to assets held for sale			0	0
Total mortgages and other loans payable			4,236,545,000	4,140,712,000
Deferred financing costs, net of amortization			(69,275,000)	(66,882,000)
Total mortgages and other loans payable, net			4,167,270,000	4,073,830,000
Book value of collateral			7,100,000,000	6,000,000,000
Series J Preferred Units
Debt Instrument [Line Items]
Total fixed rate debt			4,000,000	4,000,000
Limited partnership interest			$ 4,000,000
Preferred Units (as a percent)			3.75%
Preferred Units, liquidation preference (in dollars per unit) \| $ / shares			$ 1,000.00
Series J Preferred Units \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.75%
FHLB Advance Maturing in January 2017
Debt Instrument [Line Items]
Total fixed rate debt			$ 0	105,000,000
FHLB Advance Maturing in January 2017, 2
Debt Instrument [Line Items]
Total fixed rate debt			0	100,000,000
Unsecured Loan
Debt Instrument [Line Items]
Total fixed rate debt			$ 16,000,000	16,000,000
Unsecured Loan \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			4.81%
Master Repurchase Agreement
Debt Instrument [Line Items]
Total floating rate debt			$ 184,642,000	184,642,000
Maximum facility capacity			$ 300,000,000.0
Basis Point Fee (as a percent)	25.00%
Threshold amount for basis point fee to be applicable (less than)	$ 150,000,000.0
Master Repurchase Agreement \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)			3.28%
Master Repurchase Agreement \| Minimum \| LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)			225.00%
Master Repurchase Agreement \| Maximum \| LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)			400.00%
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt			$ 100,000,000	100,000,000
Landmark Square \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			4.90%
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 450,000,000	450,000,000
485 Lexington Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			4.41%
762 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 771,000	7,694,000
762 Madison Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.99%
One Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 509,967,000	517,806,000
One Madison Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			5.91%
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt			$ 220,161,000	221,446,000
100 Church Street \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			4.68%
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 500,000,000	500,000,000
Interest in property (as a percent)			51.00%
919 Third Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			5.12%
400 East 58th Street
Debt Instrument [Line Items]
Total fixed rate debt			$ 40,000,000	40,000,000
400 East 58th Street \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.00%
Term (in Years)			5 years
420 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 300,000,000	300,000,000
420 Lexington Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.99%
1515 Broadway
Debt Instrument [Line Items]
Total fixed rate debt			$ 884,470,000	888,531,000
1515 Broadway \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.93%
885 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt			$ 267,650,000	267,650,000
885 Third Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			6.26%
719 Seventh Avenue
Debt Instrument [Line Items]
Total floating rate debt			$ 39,521,000	37,388,000
719 Seventh Avenue \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)			3.84%
183, 187 Broadway & 5-7 Dey Street
Debt Instrument [Line Items]
Total floating rate debt			$ 58,000,000	58,000,000
183, 187 Broadway & 5-7 Dey Street \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)			3.48%
1080 Amsterdam
Debt Instrument [Line Items]
Total floating rate debt			$ 0	3,525,000
1080 Amsterdam \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)
315 West 33rd Street [Member]
Debt Instrument [Line Items]
Total fixed rate debt			$ 250,000,000	0
315 West 33rd Street [Member] \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			4.17%
220 East 42nd Street
Debt Instrument [Line Items]
Total floating rate debt			$ 275,000,000	275,000,000
220 East 42nd Street \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)			2.38%
One Vanderbilt
Debt Instrument [Line Items]
Total floating rate debt			$ 100,000,000	64,030,000
One Vanderbilt \| Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)			4.29%
One Vanderbilt \| Construction Loans
Debt Instrument [Line Items]
Term (in Years)		5 years
Number of extension options \| extenstion_option		2
Period of extension options		1 year
Maximum facility capacity		$ 1,500,000,000.0
One Vanderbilt \| Construction Loans \| LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)		350.00%
Amsterdam Avenue 1080 [Member]
Debt Instrument [Line Items]
Total fixed rate debt			$ 36,363,000	$ 0
Total fixed rate debt			35,500,000
Secured Debt, Bearing Fixed Interest, Subordinate Loan Amount			$ 900,000
Amsterdam Avenue 1080 [Member] \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.63%
Term (in Years)			5 years
Amsterdam Avenue 1080 [Member] \| Mortgage loan \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			3.50%
Amsterdam Avenue 1080 [Member] \| Subordinate loan \| Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			7.00%