Debt Instrument, Periodic Principal Payment, Percent

No definition available.

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Balance Type:	na
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

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

+ References

No definition available.

+ Details

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

- 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=114775744&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

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

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=114001942&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=114001942&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=109223946&loc=d3e3602-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(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

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_SecuredCreditFacilityRevolverDueMarch2018Member
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=star_SecuredRevolvingCreditFacilityDueSeptember2020Member
Namespace Prefix:
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Debt Obligations, net - Secured Term Loan and Credit Facility Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Aug. 31, 2016	Jun. 30, 2016	Mar. 31, 2015
Line of Credit Facility [Line Items]
Loss on early extinguishment of debt			$ 468,000	$ 372,000
2016 Senior Term Loan \| LIBOR
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)			1.00%
Secured Debt \| 2016 Senior Term Loan
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 650,000,000.0	$ 400,000,000.0			$ 500,000,000.0	$ 450,000,000.0
Percentage of par credit facilities were issued at						99.00%
Required quarterly principal payment (as a percent)			0.25%
Loss on early extinguishment of debt				$ 400,000
Secured Debt \| 2016 Senior Term Loan \| LIBOR
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)	2.75%	3.00%	2.75%
Secured Debt \| 2016 Senior Term Loan \| LIBOR \| Minimum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)		0.75%
Secured Debt \| 2016 Senior Term Loan \| LIBOR \| Maximum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)			1.75%
Secured Debt \| 2015 Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity							$ 250,000,000.0
Secured Debt \| 2015 $325 million Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 325,000,000
Maximum borrowing capacity		$ 325,000,000	$ 325,000,000
Debt instrument term (in years)			1 year
Current borrowing capacity			$ 325,000,000
Secured Debt \| 2015 $325 million Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage			0.30%
Secured Debt \| 2015 $325 million Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage			0.50%
Secured Debt \| 2015 $325 million Revolving Credit Facility \| LIBOR
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)			2.50%
Secured Debt \| 2015 $325 million Revolving Credit Facility \| LIBOR \| Minimum
Line of Credit Facility [Line Items]
Basis point spread on variable interest rate (as a percent)			1.00%