Revenue Recognition - Schedule of Changes Within Defense Segment Due to Contract Adjustments (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Abstract]
Net sales	$ 31.2	$ 63.9	$ 2.2
Operating income	16.2	44.7	2.2
Net income	$ 12.4	$ 34.5	$ 1.7
Diluted earnings per share	$ 0.18	$ 0.49	$ 0.02