Long-Term Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Total debt - principal	$ 2,949,557	$ 2,564,270	$ 2,192,563
Less unamortized debt issuance costs	16,196	16,979	20,552
Debt long term and short term less unamortized debt issuance costs combined amount	2,933,361	2,547,291	2,172,011
Less current portion	758,652	108,789	580,247
Long-term debt	2,174,709	2,438,502	1,591,764
Bank debt [Member]
Debt Instrument [Line Items]
Total debt - principal	1,268,497	903,945	400,183
5% Senior Notes due 2020 [Member]
Debt Instrument [Line Items]
Total debt - principal	$ 280,000	$ 280,000	$ 500,000
Senior note interest rate (percent)	5.00%	5.00%	5.00%
Less current portion	$ 280,000
5 1/2% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Total debt - principal	$ 300,000	$ 300,000	$ 300,000
Senior note interest rate (percent)	5.50%	5.50%	5.50%
4 3/4% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Total debt - principal	$ 300,000	$ 300,000	$ 300,000
Senior note interest rate (percent)	4.75%	4.75%	4.75%
3 1/4% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Total debt - principal	$ 801,060	$ 780,325	$ 692,380
Senior note interest rate (percent)	3.25%	3.25%	3.25%
Revolving Loan [Member] | Bank debt [Member]
Debt Instrument [Line Items]
Total debt - principal	$ 415,000	$ 0	$ 319,510
Less current portion	415,000
U S Term Loans [Member] | Bank debt [Member]
Debt Instrument [Line Items]
Total debt - principal	800,000	800,000	0
Less current portion	40,000
Canadian Term Loans [Member] | Bank debt [Member]
Debt Instrument [Line Items]
Total debt - principal	23,362	27,147	34,166
Other Foreign Bank Revolving And Term Loans [Member] | Bank debt [Member]
Debt Instrument [Line Items]
Total debt - principal	30,135	$ 76,798	$ 46,507
Less current portion	$ 23,700