Debt Instrument, Principal Amount Called For Redemption

No definition available.

Name:	star_DebtInstrumentPrincipalAmountCalledForRedemption
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the percentage of principal amount used in the computation of issue price for the line of credit facility.

+ References

No definition available.

+ Details

Name:	star_LineOfCreditFacilityIssuePriceAsPercentageOfPrincipalAmount
Namespace Prefix:	star_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

+ Details

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

- 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

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12355-112629

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12317-112629

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=star_UnsecuredDebtNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_Unsecured550SeniorNotesDueFebruary2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_Unsecured525SeniorNotesDueSeptember2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_Unsecured4.75SeniorNotesDueOctober2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_Unsecured4.625SeniorNotesDueSeptember2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_UnsecuredNotesSixPointFivePercentSeniorNotesDueJuly2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_Unsecured4.25SeniorNotesDueAugust2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_UnsecuredSixPercentSeniorNotesDueApril2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt Obligations, net - Unsecured Notes Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Jan. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Aug. 31, 2020	Nov. 30, 2019
Debt Instrument [Line Items]
Loss on early extinguishment of debt			$ 7,924,000	$ 0	$ 12,038,000	$ 468,000
Unsecured notes
Debt Instrument [Line Items]
Loss on early extinguishment of debt					$ 12,000,000.0	500,000
Unsecured notes \| 5.50% Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount							$ 400,000,000.0
Stated interest rates (as a percent)			5.50%		5.50%		5.50%
Unsecured notes \| 5.25% Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount							$ 400,000,000.0
Stated interest rates (as a percent)							5.25%
Unsecured notes \| 4.75% Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 675,000,000.0		$ 675,000,000.0		$ 100,000,000.0
Stated interest rates (as a percent)			4.75%	4.75%	4.75%	4.75%		4.75%
Percentage of par								102.00%
Yield to maturity (as a percent)								4.29%
Unsecured notes \| 4.625% senior notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 400,000,000.0		$ 400,000,000.0
Stated interest rates (as a percent)				4.625%		4.625%
Unsecured notes \| 6.50% senior notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 275,000,000.0		$ 275,000,000.0
Stated interest rates (as a percent)				6.50%		6.50%
Unsecured notes \| 4.25% Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount		$ 550,000,000.0
Stated interest rates (as a percent)		4.25%	4.25%		4.25%
Principal amount redeemed		$ 375,000,000.0
Unsecured notes \| 6.00% Senior Notes
Debt Instrument [Line Items]
Stated interest rates (as a percent)		6.00%	6.00%		6.00%
Principal amount redeemed	$ 110,500,000