Debt Instrument, Debt Issuance Allowable Period

No definition available.

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Namespace Prefix:	fast_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Maximum Face Amount Allowable

+ References

No definition available.

+ Details

Name:	fast_DebtInstrumentMaximumFaceAmountAllowable
Namespace Prefix:	fast_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Number of Debt Instrument Series

+ References

No definition available.

+ Details

Name:	fast_DebtInstrumentNumberofDebtInstrumentSeries
Namespace Prefix:	fast_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

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

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: 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 3: 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

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fast_FloatingRateNotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fast_FixedRateNotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fast_A2.00SeniorPromissoryNotePayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fast_A2.45SeniorUnsecuredPromissoryNotePayableMember
Namespace Prefix:
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Balance Type:
Period Type:

Debt Commitments and Contingencies - Senior Unsecured Promissory Notes Payable (Details)	Jul. 20, 2016 USD ($)	Sep. 30, 2016 USD ($) debt_instrument_series	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Debt		$ 445,000,000	$ 365,000,000
Senior Unsecured Promissory Notes [Member]
Debt Instrument [Line Items]
Debt issuance period after effective date	3 years
Maximum aggregate principal amount outstanding	$ 200,000,000
Number of debt instrument series \| debt_instrument_series		2
Senior Unsecured Promissory Notes [Member] \| Floating Rate Notes Payable [Member]
Debt Instrument [Line Items]
Term of debt (no later than 12 years)	10 years
Senior Unsecured Promissory Notes [Member] \| Fixed Rate Notes Payable [Member]
Debt Instrument [Line Items]
Term of debt (no later than 12 years)	12 years
Senior Unsecured Promissory Notes [Member] \| 2.00% Senior Unsecured Promissory Note Payable [Member]
Debt Instrument [Line Items]
Debt		$ 40,000,000	0
Fixed interest rate per annum		2.00%
Senior Unsecured Promissory Notes [Member] \| 2.45% Senior Unsecured Promissory Note Payable [Member]
Debt Instrument [Line Items]
Debt		$ 35,000,000	$ 0
Fixed interest rate per annum		2.45%