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v3.8.0.1

Debt - Schedule of Long-Term Debt (Parenthetical) (Detail) | 9 Months Ended
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Sep. 30, 2017
6.50% Bonds, Due 2018 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 6.50%
Debt instrument, maturity date | 2018
6.75% Notes, Due 2018 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 6.75%
Debt instrument, maturity date | 2018
5.72% Notes, Due 2019 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.72%
Debt instrument, maturity date | 2019
1.63% Convertible Notes, Due 2019 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 1.63%
Debt instrument, maturity date | 2019
6.150% Notes, Due 2020 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 6.15%
Debt instrument, maturity date | 2020
5.40% Notes, Due 2021 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.40%
Debt instrument, maturity date | 2021
5.87% Notes, Due 2022 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.87%
Debt instrument, maturity date | 2022
5.125% Notes, Due 2024 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.125%
Debt instrument, maturity date | 2024
5.90% Notes, Due 2027 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.90%
Debt instrument, maturity date | 2027
6.75% Bonds, Due 2028 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 6.75%
Debt instrument, maturity date | 2028
5.95% Notes Due 2037 [Member] |
Debt Instrument [Line Items] |
Long-term debt, interest rate | 5.95%
Debt instrument, maturity date | 2037
Iowa Finance Authority Loan, Due 2042 [Member] |
Debt Instrument [Line Items] |
Debt instrument, maturity date | 2042

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + 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(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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