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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	$ 338,398	$ 377,437	$ 1,125,968	$ 1,133,696
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	266,182	310,902	904,283	926,870
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	$ 72,216	$ 66,535	$ 221,685	$ 206,826