Name:	sir_AggregatePurchasePrice
Namespace Prefix:	sir_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

No definition available.

Name:	sir_AveragePrice
Namespace Prefix:	sir_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	sir_CommissionRate
Namespace Prefix:	sir_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	sir_NetProceedsAfterCommissionsAndSaleExpenses
Namespace Prefix:	sir_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment there

No definition available.

Name:	sir_SharesRepurchased
Namespace Prefix:	sir_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	sir_TotalSharesRepurchased
Namespace Prefix:	sir_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

No definition available.

Name:	sir_TotalSharesRepurchasedShares
Namespace Prefix:	sir_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 65
-Paragraph 15
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333

Reference 2: 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(30)(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

The cash inflow associated with the sale, maturity and collection of all investments such as debt, security and so forth during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585

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

Number of shares of stock issued attributable to transactions classified as other.

No definition available.