Loans Receivable and Other Lending Investments, net - Reserve for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Allowance for Loan Losses [Roll Forward]
Reserve for loan losses at beginning of period	$ 53,395	$ 78,489
Recovery of loan losses	(97)	(855)
Charge-offs	0	(8,168)
Reserve for loan losses at end of period	$ 53,298	$ 69,466

Allowance For Loan And Lease Loss, Recovery Of Bad Debts, Net Of (Provision For Loan And Lease Losses)

No definition available.

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

- Definition

Reflects the amount of loans that have been removed, or charged off, from both loan receivables and the reserve for credit losses, typically because they are considered to be not salvageable or have been purchased by unconsolidated collection entities.

+ References

No definition available.

+ Details

Name:	star_AllowanceForLoanLossesWriteOffs
Namespace Prefix:	star_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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