Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Feb. 22, 2018	Oct. 27, 2017	Oct. 26, 2017	Sep. 30, 2017	Aug. 02, 2017
Debt Instrument [Line Items]
Principal amount of long term debt				$ 240.7
Percentage of conversion of convertible notes	5.75%
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	$ 99.9			$ 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%