Debt - Summary of Debt (Parenthetical) (Detail)	Dec. 31, 2016	Jul. 22, 2016	Dec. 31, 2015	Apr. 17, 2014	Oct. 10, 2013	Feb. 17, 2012	Apr. 26, 2011
6.875% Senior Unsecured Notes Due 2021 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	6.875%		6.875%				6.875%
6.375% Senior Unsecured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	6.375%		6.375%			6.375%
5.750% Senior Unsecured Notes Due 2020 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	5.75%		5.75%		5.75%
4.000% Senior Unsecured Notes due 2022 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	4.00%		4.00%
5.500% Senior Unsecured Notes Due 2024 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	5.50%			5.50%
6.375% Senior Unsecured Notes due 2024 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	6.375%
5.250% Senior Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate	5.25%	5.25%