Acquisitions Acquisitions (Purchase Price Allocation) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Apr. 02, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Goodwill		$ 2,847
Payments to Acquire Businesses, Net of Cash Acquired		$ 4,960	$ 165,802	$ 98,411
ColdLight [Member]
Business Acquisition [Line Items]
Goodwill				85,300
Identifiable intangible assets				17,600
Cash				1,300
Less: cash acquired				(1,300)
Payments to Acquire Businesses, Net of Cash Acquired				$ 98,600
Vuforia [Member]
Business Acquisition [Line Items]
Goodwill			23,316
Identifiable intangible assets			41,200
Cash			4,466
Other assets and liabilities, net			261
Total allocation of purchase price consideration			69,243
Less: cash acquired			(4,466)
Total purchase price allocation, net of cash acquired			64,777
Less: contingent consideration			0
Payments to Acquire Businesses, Net of Cash Acquired			64,777
Kepware [Member]
Business Acquisition [Line Items]
Goodwill	$ 77,081		77,081
Identifiable intangible assets			34,500
Cash			590
Other assets and liabilities, net			4,729
Total allocation of purchase price consideration			116,900
Less: cash acquired			(590)
Total purchase price allocation, net of cash acquired			116,310
Less: contingent consideration			(16,900)
Payments to Acquire Businesses, Net of Cash Acquired			$ 99,410