Reportable Segments and Major Concentration Data - Pre-tax Earnings Table (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting [Abstract]
Segment operating income	$ 37,514	$ 9,393	$ 59,682	$ 35,300
Corporate operating expenses	(2,849)	(2,929)	(7,832)	(8,450)
Interest income	3	194	137	547
Interest expense	(703)	(448)	(2,002)	(1,158)
Other, net	908	268	1,561	(38)
EARNINGS BEFORE INCOME TAXES	$ 34,873	$ 6,478	$ 51,546	$ 26,201