Reportable Segments and Major Concentration Data - Pre-tax Earnings Table (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting [Abstract]
Segment operating income	$ 72,761	$ 43,072	$ 46,660
Corporate expenses	(11,437)	(10,373)	(15,076)
Interest income	142	681	418
Interest expense	(2,632)	(1,945)	(1,520)
Other, net	459	122	(102)
Earnings Before Income Taxes	$ 59,293	$ 31,557	$ 30,380