Business Combination (Details) $ in Thousands		12 Months Ended
	May 21, 2015 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Apr. 15, 2016 USD ($)
Business Acquisition [Line Items]
Cash Paid for Acquisition			$ 59,544	$ 3,113	$ 0
Goodwill Tax Basis			39,936	$ 17,249	$ 14,993
Amount From Credit Facility Used For Acquisitions			$ 20,000
Interest Rate During Period			2.50%
Goodwill Written Off Related To Sale Of Business Unit			$ 577
Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Goodwill Written Off Related To Sale Of Business Unit			577
Loss on Sale of Assets From Divestiture			821
Assets held for sale						$ 2,200
AcquisitionRelatedCostsMember
Business Acquisition Pro Forma Information Nonrecurring Adjustment [Line Items]
Business Combination Acquisition Related Costs			$ 681
Business Acquisitions
Business Acquisition [Line Items]
Number of Businesses Acquired			4
Total Consideration Transferred			$ 59,592
Cash Purchase Consideration			59,144
Cash Paid for Acquisition			58,448
Additional Consideration To Be Paid			696
Business Combination Acquired Receivables			9,000
Business Combination Acquired Receivables Estimated Uncollectible			518
Revenues From Acquisitions			34,367
Operating Income From Acquisitions			$ 3,527
Business Acquisition Southern Rewinding [Member] | Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Southern Industrial Sales and Services, Inc. (“Southern Rewinding”)
Description of Acquired Business			a Columbus, Georgia-based motor repair and related field services company
Date of Acquisition Agreement			May 21, 2015
Total Consideration Transferred	$ 3,937
Cash Purchase Consideration	3,137
Cash Paid for Acquisition			$ 400
Working Capital Transfer	$ 1,065
Business Acquisition Southern Rewinding [Member] | Infrastructure Solutions [Member] | Scenario Forecast [Member]
Business Acquisition [Line Items]
Additional Consideration To Be Paid		$ 400
Business Acquisition Technibus [Member] | Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Technibus, Inc. (“Technibus”)
Description of Acquired Business			a Canton, Ohio based provider of custom engineered, metal enclosed bus duct solutions
Date of Acquisition Agreement			Jun. 15, 2016
Goodwill Tax Basis			$ 15,305
Businessacquisition Str [Member] | Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business			STR Mechanical, LLC (“STR”)
Description of Acquired Business			We acquired 80% of the membership interests in STR, a Charlotte, North Carolina-based provider of commercial and industrial mechanical services, including maintenance, repair, and replacement services, and temperature control system installations
Minority Interest Ownership Percentage By Parent			80.00%
Date of Acquisition Agreement			Apr. 27, 2016
Business Acquisition Calumet [Member] | Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Calumet Armature & Electric, LLC (“Calumet”)
Description of Acquired Business			an Illinois-based provider of design, manufacturing, assembly, and repair services of electric motors for the industrial and mass transit markets
Date of Acquisition Agreement			Oct. 30, 2015
Minimum Contingent Consideration Value			$ 448
Contingent Consideration Fair Value			1,100
Maximum Contingent Consideration Value			$ 2,250
Business Acquisition Shanahan [Member] | Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Shanahan Mechanical and Electrical, Inc. (“Shanahan”)
Description of Acquired Business			a Nebraska-based provider of mechanical and electrical contracting services
Date of Acquisition Agreement			Nov. 20, 2015