Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions			3 Months Ended	6 Months Ended
		Feb. 10, 2021	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from sale of business	[1],[2]			$ 837.0	$ 0.0
Interior Products [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Loss on sale			$ 2.4	357.8
Consolidated goodwill balance included in carrying value of net assets				$ 730.9
Stock Purchase Agreement [Member] | Interior Products [Member] | FBM [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from sale of business		$ 850.0

[1] See Note 3 for additional information.

[2] Unless otherwise noted, amounts include both continuing and discontinued operations.