Stock-Based Compensation Plans and Employee Benefits (401(k) Plan) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Requisite service period	3 months
Defined contribution plan maximum percentage of matching contribution	50.00%
Defined contribution plan maximum percentage of employee compensation	10.00%
Gross contributions made by the Company	$ 1.0	$ 1.0	$ 0.9

Represents the maximum percentage of a participant's annual compensation upon which the matching Company contribution is based.

No definition available.

+ Details

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

- Definition

At the discretion of the Board of Directors, represents the maximum percentage matching contribution which the Company may make of the first ten percent of the participant's annual compensation.

+ References

No definition available.

+ Details

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

- Definition

Represents the period of continuous service with the Company required in order to be eligible to participate in the 401(k) Plan.

+ References

No definition available.

+ Details

Name:	star_DefinedContributionPlanServiceRequirement
Namespace Prefix:	star_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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