Acquisitions (Narrative) (Details) $ in Thousands			1 Months Ended						3 Months Ended								12 Months Ended
	Mar. 14, 2018 USD ($)	May 08, 2017 USD ($)	Aug. 30, 2017 USD ($)	May 25, 2017 USD ($)	Nov. 07, 2016 USD ($) a	Sep. 02, 2016 USD ($)	Jan. 29, 2016 USD ($)	Oct. 16, 2015 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired		$ 38,600			$ 75,000												$ 11,445	$ 198,628	$ 82,062
Payments to Acquire Businesses, Gross			$ 36,000	$ 48,800		$ 41,000	$ 31,600	$ 10,500
Goodwill	$ 3,500	7,500	10,700	4,800	30,100		10,200		$ 381,652				$ 377,879				381,652	377,879	323,600
Business Combination, Contingent Consideration, Liability							2,700
Revenues	8,000	45,000	14,000	25,000	40,000	25,000	35,000		$ 231,086	$ 192,223	$ 174,778	$ 173,495	$ 207,005	$ 171,189	$ 161,178	$ 146,368	$ 771,582	$ 685,740	$ 571,459
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					4,800	28,300
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings			18,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		17,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	200	9,400	300	1,700	16,600	4,600	9,600
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities					$ 15,700
Area of Land | a					130,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		4,100	1,800	2,500	$ 7,400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	1,100	5,100	2,100	5,200	11,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Capital Lease Obligation		8,900			2,800
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		400		400	9,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	400	4,300	200	4,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	1,200	8,100	$ 3,200	35,600
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 1,500
Customer Relationships [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					$ 32,800
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					20 years
Fremont Plastics, Inc [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings								$ 2,000
Plastique Group Limited [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill							$ 11,900
Westland Technologies, Inc [Member]
Business Acquisition [Line Items]
Goodwill						17,300
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities						$ 9,500
Mayday Manufacturing Co [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets					$ 300
Morgan Schaffer Inc [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				$ 3,600
Morgan Schaffer Inc [Member] | Customer Relationships and Developed Technology [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				10 years
NRG Systems Inc [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		14 years
Vanguard Instruments Company [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			15 years
Manta Test Systems Inc [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	9,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings	3,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	$ 400
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	13 years