Acquisitions (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended								12 Months Ended
	Sep. 02, 2016	Jan. 29, 2016	Oct. 16, 2015	Jan. 28, 2015	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition [Line Items]
Goodwill					$ 323,616				$ 291,157				$ 323,616	$ 291,157	$ 282,300
Revenue, Net					$ 159,505	$ 140,191	$ 138,930	$ 132,833	$ 153,612	$ 134,191	$ 128,941	$ 120,547	$ 571,459	$ 537,291	$ 531,120
Enoserv LLC [Member]
Business Acquisition [Line Items]
Goodwill				$ 10,000
Revenues				8,000
Business Combination, Consideration Transferred, Total				20,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total				$ 9,000
Fremont Plastics, Inc [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 10,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings			$ 2,000
Plastique Group Limited [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 31,600
Goodwill		10,200
Business Combination, Contingent Consideration, Liability		2,700
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total		11,900
Revenue, Net		35,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment, Total		$ 9,600
Westland Technologies, Inc [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 41,000
Goodwill	17,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total	28,300
Revenue, Net	25,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment, Total	5,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities	$ 10,400