Financial Information for the Company and Its Subsidiaries - Additional Information (Detail)	Sep. 30, 2021	Dec. 31, 2020	Feb. 16, 2016	Sep. 21, 2015	Feb. 11, 2015
5.500% Senior Notes Due 2028 [Member]
Line of Credit Facility [Line Items]
Debt instrument interest rate	5.50%
5.000% Senior Notes Due 2029 [Member]
Line of Credit Facility [Line Items]
Debt instrument interest rate	5.00%
5.625% Senior Notes Due 2023 [Member]
Line of Credit Facility [Line Items]
Debt instrument interest rate	5.625%	5.625%		5.625%	5.625%
6.500% Senior Notes Due 2024 [Member]
Line of Credit Facility [Line Items]
Debt instrument interest rate	6.50%	6.50%	6.50%