Derivatives (Classification on the Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest Expense \| Interest rate swaps \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	$ 15	$ 126		$ (568)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	(16)	(19)		(17)
Interest Expense \| Interest rate cap \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)			$ 439	0
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)			339	(185)
Earnings from equity method investments \| Interest rate swaps \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(69)	124	(85)	(500)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	(38)	(92)	(188)	(284)
Earnings from equity method investments \| Interest rate cap \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(2)	(1)	(16)	(2)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	(2)	(1)	(16)	0
Earnings from equity method investments \| Foreign exchange contracts \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(1)	(150)	(371)	(199)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	0	0	0	0
Other Expense \| Interest rate cap \| Not designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain or (Loss) Recognized in Income	0	(4)	6	(1,059)
Other Expense \| Foreign exchange contracts \| Not designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain or (Loss) Recognized in Income	$ (199)	$ 65	$ (970)	$ 406

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

+ Details

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

- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959

+ Details

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

- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

+ Details

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

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InterestExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=star_EarningsfromEquityMethodInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OtherExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: