Schedule of Debt Obligations (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Mar. 14, 2019	Dec. 31, 2018	Sep. 30, 2018	Feb. 22, 2018	Oct. 27, 2017	Sep. 30, 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%		5.75%
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		$ 109.7		$ 125.0
Percentage of conversion of convertible notes	5.75%		5.75%	5.75%	5.75%