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Business Combinations - Additional Information (Detail)
$ in Thousands
12 Months Ended
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
Business Acquisition [Line Items]      
Number of businesses acquired 0    
Goodwill $ 804,414 $ 798,415 $ 814,750
QuadMetrics      
Business Acquisition [Line Items]      
Common stock acquired   100.00%  
Cash consideration   $ 5,700  
Intangible assets acquired   $ 2,000  
Weighted average useful life   4 years  
Goodwill   $ 3,900  
TONBELLER      
Business Acquisition [Line Items]      
Common stock acquired     100.00%
Cash consideration     $ 59,600
Intangible assets acquired     $ 14,900
Weighted average useful life     4 years 11 months
Goodwill     $ 46,100