Segment and Geographic Information and Significant Customers (Classification of Revenue by Major Geographic Areas) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	$ 449,197	$ 449,449	$ 1,352,434	$ 1,362,866
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	337,411	333,809	1,019,945	1,014,295
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	$ 111,786	$ 115,640	$ 332,489	$ 348,571