Commitments and Contingencies (Narrative) (Details)	6 Months Ended
Mar. 31, 2016 USD ($)
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 451,100,000
Liquidated damages	8,900,000
Probable liquidated damages	2,000,000
Loss contingency, estimate of actual or projected loss	1,600,000
Facility Agreement \| Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	2,800,000
Revolving credit facility	14,400,000
Amount of credit facility remaining borrowing capacity	11,600,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	24,700,000
Surety Bonds
Guarantee Obligations [Line Items]
Guarantee liability	$ 298,900,000

Commitments and contingencies additional bonding capacity.

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- Definition

Loss contingency probable loss in period.

+ References

No definition available.

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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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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.

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No definition available.

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- Definition

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.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

+ References

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
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-Section 50
-Paragraph 9
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-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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- Definition

The amount of loss pertaining to the specified contingency that was charged against earnings in the period, including the effects of revisions in previously reported estimates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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