Name:	fstr_CarryoverOfAssetSalesAllowed
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Market valuation of entity divided by earnings before interest, taxes, depreciation, and amortization (EBITDA) required.

No definition available.

Name:	fstr_EbitdaRequired
Namespace Prefix:	fstr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Market valuation of entity divided by earnings before interest, taxes, depreciation, and amortization (EBITDA) required at seventh quarter of the credit agreement.

No definition available.

Name:	fstr_EbitdaRequiredForSeventhQuarter
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Required ratio of fixed charges to the last twelve months of EBITDA.

No definition available.

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Data Type:	xbrli:pureItemType
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Required ratio of fixed charges to the last twelve months of EBITDA after the fifth quarter of credit agreement.

No definition available.

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Data Type:	xbrli:pureItemType
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Period Type:	duration

Leverage ratio in effect for the seventh quarter of a credit agreement.

No definition available.

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Data Type:	xbrli:pureItemType
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Leverage ratio in effect for the eighth quarter and remainder of a credit agreement.

No definition available.

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Data Type:	xbrli:pureItemType
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Required amount of undrawn availability of a debt instrument.

No definition available.

Name:	fstr_LiquidityCovenant
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Maximum amount allowed of loans and advances to non-loan parties and loans, advances, and investments by domestic loan parties to subsidiaries that are not loan parties and to foreign loan parties.

No definition available.

Name:	fstr_LoansAndAdvancesLimit
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Maximum amount of asset sales allowed under a loan agreement.

No definition available.

Name:	fstr_MaximumAssetSalesAllowed
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amount of restriction on the entity's ability to pay dividends, distributions, or redemptions as required by the terms of the credit facility when funds are drawn from the facility.

No definition available.

Name:	fstr_MaximumDividendsAllowed
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

Reference 1: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

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.

No definition available.

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

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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

Including the current and noncurrent portions, aggregate carrying value as of the balance sheet date of loans payable (with maturities initially due after one year or beyond the operating cycle if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16)(a)(2))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

Name:	us-gaap_LineOfCreditFacilityAxis=fstr_PncBankN.a.BankOfAmericaN.a.WellsFargoBankN.a.CitizensBankOfPennsylvaniaAndBranchBankingAndTrustCompanyMember
Namespace Prefix:
Data Type:	na
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Period Type:

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	fstr_TierAxis=fstr_LowestTierMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
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