Estimated Fair Values of Other Financial Instruments (Parenthetical) (Detail)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Feb. 22, 2019	Feb. 22, 2018	Sep. 30, 2017
5.75% Senior Subordinated Notes Due August 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of conversion of convertible notes	5.75%		5.75%
Convertible Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of conversion of convertible notes						1.50%
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of conversion of convertible notes	5.75%	5.75%	5.75%	5.75%	5.75%