Business Combinations (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Cash Paid for Acquisition			$ 14,659	$ 59,698
Contingent Consideration Fair Value	$ 1,347		$ 1,347		$ 1,100
2017 Business Acquisitions [Member]
Business Acquisition [Line Items]
Number Of Businesses Acquired			2
Total Consideration Transferred			$ 15,871
Cash Purchase Consideration			15,139
Cash Paid for Acquisition			14,739
Additional Consideration To Be Paid			400
Contingent Consideration Fair Value	732		732
Revenues From Acquisitions	5,649		7,047
Operating Income From Acquisitions	(104)		(150)
2016 Business Acquisitions [Member]
Business Acquisition [Line Items]
Number Of Businesses Acquired				4
Total Consideration Transferred				$ 59,592
Contingent Consideration Fair Value	614		614
Contingent Consideration Payment			$ 535
Revenues From Acquisitions		$ 10,649		19,613
Operating Income From Acquisitions		$ 1,193		$ 1,841
Business Acquisition Technibus [Member] | Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Technibus, Inc.
Description of Acquired Business			a Canton, Ohio based provider of custom engineered, metal enclosed bus duct solutions
Date of Acquisition Agreement			Jun. 15, 2016
Business Acquisition STR [Member] | Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business			STR Mechanical, LLC
Description of Acquired Business			a Charlotte, North Carolina-based provider of commercial and industrial mechanical services
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
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
Contingent Consideration Fair Value	$ 614		$ 614		$ 1,100
Contingent Consideration Payment			$ 535
Business Acquisition Shanahan [Member] | Commercial & Industrial [Member]
Business Acquisition [Line Items]
Name of Acquired Business			Shanahan Mechanical and Electrical, Inc.
Description of Acquired Business			a Nebraska-based provider of mechanical and electrical contracting services
Date of Acquisition Agreement			Nov. 20, 2015
Freeman Acquisition [Member] | Infrastructure Solutions [Member]
Business Acquisition [Line Items]
Date of Acquisition Agreement			Mar. 16, 2017
Technical Services Acquisition [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