Schedule of Debt Obligations (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 14, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Feb. 22, 2018	Oct. 27, 2017
Debt Instrument [Line Items]
Principal amount of long term debt							$ 240.7
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%	5.75%			5.75%
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	$ 105.7		$ 109.7			$ 125.0
Debt instrument, interest rate, stated percentage	5.75%		5.75%		5.75%	5.75%