Represents the number of foreign countries (excluding Canada) in which the entity has exploratory and development interests.

Name:	fst_ExploratoryAndDevelopmentInterestsInForeignCountriesNumber
Namespace Prefix:	fst
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum percentage of shares that could be issued or sold by the subsidiary or equity method investee per stock transaction.

+ Details

Name:	fst_SaleOfStockMaximumPercentageOfSharesIssuedInTransaction
Namespace Prefix:	fst
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares of common stock issued as dividends during the period. Excludes stock splits.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

+ Details

Name:	us-gaap_CommonStockDividendsShares
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section H

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_SubsidiarySaleOfStockLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

ORGANIZATION AND BASIS OF PRESENTATION (Details) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2011
Organization and Spin-off of Subsidiary
Exploratory and development interests in foreign countries (in ones)			2
Lone Pine Resources Inc [MEMBER] \| Initial Public Offering
Organization and Spin-off of Subsidiary
Percentage of common stock sold (as a percent)		19.90%
Number of shares of common stock sold (in shares)	15
Number of shares of common stock held by entity distributed in spin-off (in shares)			70