Debt - Summary of Debt (Parenthetical) (Detail) $ in Thousands, £ in Millions		Sep. 30, 2017 USD ($)	Sep. 30, 2017 GBP (£)	Sep. 07, 2017	Mar. 24, 2017	Mar. 04, 2017	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Debt		$ 4,876,759
6.375% Senior Unsecured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		6.375%	6.375%				6.375%
Debt		$ 350,000					$ 350,000
5.750% Senior Unsecured Notes Due 2020 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		5.75%	5.75%			5.75%	5.75%
Debt	[1]						$ 210,340
4.000% Senior Unsecured Notes due 2022 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		4.00%	4.00%				4.00%
Debt	[1]	$ 590,700					$ 525,850
5.500% Senior Unsecured Notes Due 2024 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		5.50%	5.50%				5.50%
Debt		$ 300,000					$ 300,000
6.375% Senior Unsecured Notes due 2024 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		6.375%	6.375%				6.375%
Debt		$ 500,000					$ 500,000
3.325% Senior Unsecured Notes Due 2025 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		3.325%	3.325%		3.325%		3.325%
Debt	[1]	$ 590,700
5.250% Senior Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		5.25%	5.25%				5.25%
Debt		$ 500,000					$ 500,000
5.000% Senior Unsecured Notes Due 2027 [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate		5.00%	5.00%	5.00%			5.00%
Debt		$ 1,400,000
GBP-denominated Borrowings [Member]
Debt Instrument [Line Items]
Debt | £			£ 4

[1] These notes are Euro-denominated and reflect the exchange rate at September 30, 2017 and December 31, 2016, respectively.