Schedule of Impact on Earnings Per Share Calculation (Parenthetical) (Detail)	Sep. 30, 2019	Mar. 14, 2019	Dec. 31, 2018	Sep. 30, 2018	Feb. 22, 2018	Sep. 30, 2017
Earnings Per Share Disclosure [Line Items]
Percentage of conversion of convertible notes				5.75%
5.75% Senior Subordinated Notes Due August 2023
Earnings Per Share Disclosure [Line Items]
Percentage of conversion of convertible notes	5.75%	5.75%		5.75%
Convertible Notes
Earnings Per Share Disclosure [Line Items]
Percentage of conversion of convertible notes						1.50%
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023
Earnings Per Share Disclosure [Line Items]
Percentage of conversion of convertible notes	5.75%		5.75%	5.75%	5.75%