Borrowings - Components of Long-Term Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 20, 2017	Dec. 31, 2015	May 21, 2014
Line Of Credit Facility [Line Items]
Long-term debt, Gross	$ 2,270,000	$ 1,046,076
Less: Unamortized debt discount on 3.875% Convertible Senior Subordinated Notes due 2017	0	(2,707)
Less: Unamortized debt issuance costs	(20,448)	(10,046)
Net carrying amount	2,249,552	1,033,323
Current portion of borrowings	(86,625)	(183,071)
Long-term borrowings	$ 2,162,927	$ 850,252
Interest rate	3.875%	3.875%		3.875%
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Revolving credit facility, at a rate of 3.44% at December 31, 2017 and 2.27% at December 31, 2016, due 2022	$ 349,000	$ 210,000
Senior credit facility interest rate	3.44%	2.27%
Debt maturity date	Jul. 16, 2018
Securitization Program
Line Of Credit Facility [Line Items]
Securitization program, at a rate of 2.31% at December 31, 2017 and 1.52% at December 31, 2016	$ 50,000	$ 50,000
Interest rate	2.31%	1.52%
Term loan facility, at a rate of 3.57% at December 31, 2017, due 2022 | Term Loan
Line Of Credit Facility [Line Items]
Revolving credit facility, at a rate of 3.44% at December 31, 2017 and 2.27% at December 31, 2016, due 2022	$ 721,000	$ 0
Senior credit facility interest rate	3.57%
3.875% Convertible Senior Subordinated Notes due 2017 | Senior Notes
Line Of Credit Facility [Line Items]
3.875% Convertible Senior Subordinated Notes due 2017	$ 0	$ 136,076
Interest rate	3.875%	3.875%
5.25% Senior Notes due 2024 | Senior Notes
Line Of Credit Facility [Line Items]
Senior notes	$ 250,000	$ 250,000			$ 250,000
Senior credit facility interest rate		3.57%
Interest rate	5.25%	5.25%			5.25%
4.875% Senior Notes due 2026 | Senior Notes
Line Of Credit Facility [Line Items]
Senior notes	$ 400,000	$ 400,000
Interest rate	4.875%	4.875%
4.625% Senior Notes due 2027 | Senior Notes
Line Of Credit Facility [Line Items]
Senior notes	$ 500,000	$ 0	$ 500,000
Interest rate	4.625%	4.625%	4.625%