Acquisitions (Narrative) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Apr. 02, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) employee	Sep. 30, 2015 USD ($)	Jan. 12, 2016 USD ($)	Nov. 03, 2015 USD ($)
Acquisition-related cost		$ 1,600	$ 3,500	$ 8,900
Payments to Acquire Businesses, Net of Cash Acquired		4,960	165,802	98,411
Goodwill acquired		2,847
Revenue, Net		1,164,039	1,140,533	1,255,242
Costs and Expenses		$ 794,122	851,882	878,892
ColdLight [Member]
Payments to Acquire Businesses, Net of Cash Acquired				98,600
Acquisition of businesses, net cash acquired				1,300
Goodwill acquired				85,300
Finite-lived Intangible Assets Acquired				17,600
Kepware [Member]
Payments to Acquire Businesses, Net of Cash Acquired			99,410
Acquisition of businesses, net cash acquired			590
Goodwill acquired	$ 77,081		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] | ColdLight [Member]
Finite-lived Intangible Assets Acquired				$ 13,600
Weighted average useful lives of acquired intangible assets				10 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] | ColdLight [Member]
Finite-lived Intangible Assets Acquired				$ 3,500
Weighted average useful lives of acquired intangible assets				9 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] | ColdLight [Member]
Finite-lived Intangible Assets Acquired				$ 500
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		10 years
Trademarks [Member] | ColdLight [Member]
Weighted average useful lives of acquired intangible assets				7 years
Line of Credit [Member]
Credit facility, borrowings outstanding		$ 218,125	$ 258,125
Line of Credit [Member] | Kepware [Member]
Credit facility, borrowings outstanding					$ 100,000
Line of Credit [Member] | Vuforia [Member]
Credit facility, borrowings outstanding						$ 50,000