Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Feb. 22, 2018	Oct. 27, 2017	Oct. 26, 2017	Sep. 30, 2017	Aug. 02, 2017	Jun. 30, 2017	Nov. 29, 2012
Debt Instrument [Line Items]
Principal amount of long term debt			$ 240.7				$ 0.0
Debt instrument, interest rate, stated percentage	5.75%
5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.75%
Variable Funding Notes
Debt Instrument [Line Items]
Principal amount of long term debt	$ 100.0							$ 100.0
Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt	$ 190.4		$ 57.8	$ 300.0		$ 300.0
Convertible Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.50%
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Principal amount of long term debt	$ 111.0	$ 125.0
Debt instrument, interest rate, stated percentage	5.75%	5.75%			5.75%