Name:	ck0000790528_DebtInstrumentOptionalRedemptionPricePercentage
Namespace Prefix:	ck0000790528_
Data Type:	num:percentItemType
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Period Type:	duration

The percentage of the principal amount at which, the 2017 and 2018 notes are redeemable prior to the redemption date, together with accrued and unpaid interest, if any, to the redemption date, plus a make-whole premium.

No definition available.

Name:	ck0000790528_DebtInstrumentsEarlyRedemptionPriceAsPercentageOfPrincipalAmount
Namespace Prefix:	ck0000790528_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The date on or after which the notes will become redeemable by the Company, in whole or in part, at specified redemption prices.

No definition available.

Name:	ck0000790528_DebtInstrumentsRedemptionDate
Namespace Prefix:	ck0000790528_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	instant

The percentage of the principal amount at which, the 2017 and 2018 notes are redeemable prior to the redemption date, together with accrued and unpaid interest.

No definition available.

Name:	ck0000790528_DebtInstrumentsRedemptionPriceAsPercentageOfPrincipalAmount
Namespace Prefix:	ck0000790528_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The extent of future net income that the Company may pay dividends to its parent company, subject to certain exceptions.

No definition available.

Name:	ck0000790528_DividendPaymentThresholdOfPercentageOfFutureNetIncome
Namespace Prefix:	ck0000790528_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The portion of the notes that the Company may redeem prior to the debt instrument redemption date with net cash proceeds from certain equity offerings.

No definition available.

Name:	ck0000790528_OptionalRedemptionPriorToMaturityAdditionalPercentageOfPrincipal
Namespace Prefix:	ck0000790528_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

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

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682