Segment and Geographic Information and Significant Customers (Classification of Revenue by Major Geographic Areas) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Document Period End Date	Dec. 31, 2018
Segment Revenues	$ 493,654	$ 447,224
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	383,429	338,482
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Segment Revenues	$ 110,225	$ 108,742