Seasonal Financing and Debt - Long-Term Debt Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	$ 250,000
2019	500,000
2020	250,000
2021	350,000
2022	0
Thereafter	1,800,000
Long-term debt	3,150,000	$ 2,150,000
2010 Senior Notes due October 2020 and October 2040
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	0
2019	0
2020	250,000
2021	0
2022	0
Thereafter	250,000
Long-term debt	500,000
2011 Senior Notes due November 2041
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	0
2019	0
2020	0
2021	0
2022	0
Thereafter	300,000
Long-term debt	300,000
2013 Senior Notes due March 2018 and March 2023
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	250,000
2019	0
2020	0
2021	0
2022	0
Thereafter	250,000
Long-term debt	500,000
2014 Senior Notes due May 2019
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	0
2019	500,000
2020	0
2021	0
2022	0
Thereafter	0
Long-term debt	500,000
2016 Senior Notes due August 2021
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	0
2019	0
2020	0
2021	350,000
2022
Thereafter	0
Long-term debt	350,000
2017 Senior Notes due December 2025
Long Term Debt Maturities Repayments Of Principal [Line Items]
2018	0
2019	0
2020	0
2021	0
2022	0
Thereafter	1,000,000
Long-term debt	$ 1,000,000

Long Term Debt Maturities Repayments Of Principal [Line Items]

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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