Leases - Schedule of Lease Assets and Liabilities Included on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Operating Leases:
Operating lease right-of-use assets	$ 38.9	$ 33.9	$ 36.3
Current maturities of operating lease right-of-use assets	10.0	9.1	9.6
Operating lease right-of-use liabilities, less current maturities	28.9	24.9	27.0
Total operating lease liabilities	38.9	34.0	36.6
Finance Leases:
Gross property, plant and equipment	12.5	11.1	11.1
Accumulated depreciation	(7.1)	(6.3)	(6.0)
Property, plant and equipment, net	$ 5.4	$ 4.8	$ 5.1
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	us-gaap:OtherAssets	us-gaap:OtherAssets	us-gaap:OtherAssets
Current maturities of long-term lease liabilities	$ 1.4	$ 1.4	$ 1.5
Long-term lease liabilities, less current maturities	2.2	1.9	2.2
Total finance lease liabilities	$ 3.6	$ 3.3	$ 3.7