Condensed Consolidating Guarantor Financial Statements - Additional information (Detail) (2017 and 2018 Notes [Member])	9 Months Ended
Sep. 30, 2014
2017 and 2018 Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Ownership percentage	100.00%
Dividend payment threshold of percentage of future net income	50.00%

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