Indebtedness - Summary of Debt Exchange Offer to Exchange Senior Subordinated Notes (Parenthetical) (Detail)	Dec. 31, 2017	Oct. 05, 2017	Dec. 31, 2016	Sep. 30, 2016	Sep. 16, 2016
5.00% Senior Notes Due 2023
Debt Instrument [Line Items]
Interest rate on notes	5.00%	5.00%	5.00%	5.00%	5.00%
5.00% Senior Notes Due 2022
Debt Instrument [Line Items]
Interest rate on notes	5.00%	5.00%	5.00%	5.00%	5.00%
5.75% Senior Notes Due 2021
Debt Instrument [Line Items]
Interest rate on notes	5.75%	5.75%	5.75%	5.75%	5.75%