Name:	star_DiscretionaryFundings
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the off-balance sheet maximum other commitments of the entity.

No definition available.

Name:	star_OtherCommitments
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the percentage of capital committed to strategic investments by the entity that may be drawn down.

No definition available.

Name:	star_PercentageOfCapitalCommittedThatMayBeDrawnDown
Namespace Prefix:	star_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the off-balance sheet unfunded maximum amount of funds for construction and development loans and build-outs of space in net lease assets over a period of time if and when the borrowers and tenants meet established milestones and other performance criteria.

No definition available.

Name:	star_PerformanceBasedCommitments
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents certain off-balance sheet unfunded commitments of the entity.

No definition available.

Name:	star_UnfundedCommitments
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Name:	star_UnfundedFinancialCommitmentsLineItems
Namespace Prefix:	star_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

Name:	star_UnfundedFinancialCommitmentsAxis=us-gaap_LoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	star_UnfundedFinancialCommitmentsAxis=us-gaap_OtherInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: