Business Combinations (Details) $ in Thousands	6 Months Ended
Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)
Business Acquisition [Line Items]
Contingent Consideration Fair Value	$ 467	$ 786
2017 Business Acquisitions [Member]
Business Acquisition [Line Items]
Number Of Businesses Acquired	3
Total Consideration Transferred	$ 20,979
Business Acquisition Freeman [Member] \| Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Name of Acquired Business	Freeman Enclosure Systems, LLC
Description of Acquired Business	ability to manufacture custom generator enclosures
Date of Acquisition Agreement	Mar. 16, 2017
Business Acquisition Technical Services [Member] \| Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business	Technical Services II, LLC
Description of Acquired Business	a Chesapeake, Virginia-based provider of mechanical maintenance services, including commercial heating, ventilation and air conditioning, food service equipment, electrical and plumbing services
Date of Acquisition Agreement	Jun. 15, 2017
Minority Interest Ownership Percentage By Parent	80.00%
Business Acquisition NEXT [Member] \| Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business	NEXT Electric, LLC
Description of Acquired Business	a Milwaukee, Wisconsin-based electrical contractor specializing in the design, installation and maintenance of electrical systems for commercial, industrial, healthcare, water treatment and education end markets
Date of Acquisition Agreement	Jul. 14, 2017
Minority Interest Ownership Percentage By Parent	80.00%

Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

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- Definition

With respect to a business combination completed during the period, this element provides a description of the business, other than the name, which may include the industry, size, products and other important information.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
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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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Name of the acquired entity.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

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-Name Accounting Standards Codification
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-SubTopic 30
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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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The number of businesses acquired by the entity during the period.

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