Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Feb. 22, 2019	Feb. 22, 2018	Oct. 27, 2017	Oct. 26, 2017	Sep. 30, 2017	Aug. 02, 2017
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2043-01
Principal amount of long term debt						$ 240.7
5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Percentage of conversion of convertible notes	5.75%		5.75%
Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt	$ 83.2					$ 57.8	$ 300.0		$ 300.0
Convertible Notes
Debt Instrument [Line Items]
Percentage of conversion of convertible notes								1.50%
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Principal amount of long term debt	$ 94.4	$ 94.4			$ 125.0
Percentage of conversion of convertible notes	5.75%	5.75%	5.75%	5.75%	5.75%