Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value [Member]
Financial assets:
Investments and other assets	$ 1.2	$ 1.2
Financial liabilities:
Long-term debt (including current portion)	833.2	799.2
Carrying Value [Member]
Financial assets:
Investments and other assets	1.2	1.2
Financial liabilities:
Long-term debt (including current portion)	$ 818.2	$ 784.2