Acquisition (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Jan. 22, 2018	Oct. 20, 2017	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Goodwill			$ 155,982	$ 131,995	$ 129,921	$ 109,448
TempAlert
Business Acquisition [Line Items]
Cash		$ 40,741
Fair value of contingent consideration on acquired business		0
Total purchase price consideration		40,741
Fair value of net tangible assets acquired		(1,111)
Goodwill		17,552
Total assets acquired and liabilities assumed		40,741
Accelerated
Business Acquisition [Line Items]
Cash	$ 16,759
Fair value of contingent consideration on acquired business	2,300
Total purchase price consideration	19,059
Fair value of net tangible assets acquired	697
Goodwill	6,062
Total assets acquired and liabilities assumed	19,059
Customer relationships | TempAlert
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired		18,300
Customer relationships | Accelerated
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired	6,500
Purchased and core technology | TempAlert
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired		4,000
Purchased and core technology | Accelerated
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired	3,000
Trade name and trademarks | TempAlert
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired		$ 2,000
Trade name and trademarks | Accelerated
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired	1,000
Order backlog | Accelerated
Business Acquisition [Line Items]
Fair value of identifiable intangible assets acquired	$ 1,800