Acquisitions (Narrative) (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) employee	Jan. 12, 2016 USD ($)	Nov. 03, 2015 USD ($)
Acquisition-related cost	$ 500	$ 1,600	$ 3,500
Payments to Acquire Businesses, Net of Cash Acquired	3,000	4,960	165,802
Goodwill acquired	4,350	2,847
Revenue, Net	1,241,824	1,164,039	1,140,533
Costs and Expenses	$ 842,393	794,122	851,882
Kepware [Member]
Payments to Acquire Businesses, Net of Cash Acquired			99,410
Acquisition of businesses, net cash acquired			590
Goodwill acquired			77,081
Finite-lived Intangible Assets Acquired			34,500
Business acquisition, acquired net assets excluding goodwill, intangible assets and cash			4,729
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, Low			16,900
Revenue, Net			16,000
Costs and Expenses			15,000
Vuforia [Member]
Payments to Acquire Businesses, Net of Cash Acquired			64,777
Acquisition of businesses, net cash acquired			4,466
Goodwill acquired			23,316
Finite-lived Intangible Assets Acquired			41,200
Business acquisition, acquired net assets excluding goodwill, intangible assets and cash			$ 261
Weighted average useful lives of acquired intangible assets			6 years
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, Low			$ 0
Number of employees in acquired entity | employee			80
Purchased Software [Member]
Weighted average useful lives of acquired intangible assets	9 years
Purchased Software [Member] | Kepware [Member]
Finite-lived Intangible Assets Acquired			$ 28,700
Weighted average useful lives of acquired intangible assets			10 years
Customer Lists [Member]
Weighted average useful lives of acquired intangible assets	10 years
Customer Lists [Member] | Kepware [Member]
Finite-lived Intangible Assets Acquired			$ 5,200
Weighted average useful lives of acquired intangible assets			10 years
Trademarks and Trade Names [Member] | Kepware [Member]
Finite-lived Intangible Assets Acquired			$ 600
Weighted average useful lives of acquired intangible assets			6 years
Trademarks [Member]
Weighted average useful lives of acquired intangible assets	11 years
Line of Credit [Member]
Credit facility, borrowings outstanding	$ 148,125	$ 218,125
Line of Credit [Member] | Kepware [Member]
Credit facility, borrowings outstanding				$ 100,000
Line of Credit [Member] | Vuforia [Member]
Credit facility, borrowings outstanding					$ 50,000