Debt - Selected Information about Debt Issues (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Par Value	$ 1,690,612,000
Less current maturity of term loan, par value	0
Total long-term debt, par value	1,690,612,000
Total short-term debt, par value	280,000,000
Total debt, par value	1,970,612,000
Book Value	1,667,506,000	$ 1,358,363,000
Less current maturity of term loan, book value	0	9,375,000
Total long-term debt, book value	1,667,506,000	1,348,988,000
Total short-term debt, book value	279,758,000	298,738,000
Total debt, book value	1,947,264,000	1,647,726,000
Fair Value	1,842,164,000
Less current maturity of term loan, fair value	0
Total long-term debt, fair value	1,842,164,000	1,473,364,000
Total short-term debt, fair value	279,758,000
Total debt, fair value	2,121,922,000
Commercial Paper
Debt Instrument [Line Items]
Total short-term debt, par value	280,000,000
Total short-term debt, book value	279,758,000	289,363,000
Total short-term debt, fair value	$ 279,758,000
Notes, Due 5/15/23
Debt Instrument [Line Items]
Coupon Rate	7.875%
Par Value	$ 165,612,000
Book Value	164,892,000	164,713,000
Fair Value	$ 194,604,000
Senior Notes Due 2022
Debt Instrument [Line Items]
Coupon Rate	3.80%
Par Value	$ 150,000,000
Book Value	149,331,000	149,089,000
Fair Value	159,212,000
Senior Notes Due 2022 \| Consolidation eliminations \| Subsidiaries
Debt Instrument [Line Items]
Par Value	150,000,000
Book Value	$ 150,000,000
Senior Notes, Due 2028
Debt Instrument [Line Items]
Coupon Rate	4.55%
Par Value	$ 550,000,000
Book Value	544,179,000	543,735,000
Fair Value	$ 655,501,000
Senior Notes, Due 2030
Debt Instrument [Line Items]
Coupon Rate	2.15%
Par Value	$ 400,000,000
Book Value	395,091,000	0
Fair Value	$ 401,152,000
Junior Subordinated Debentures Due 2056
Debt Instrument [Line Items]
Coupon Rate	6.125%
Par Value	$ 300,000,000
Book Value	290,635,000	290,584,000
Fair Value	$ 308,760,000
Junior Subordinated Debentures Due 2057
Debt Instrument [Line Items]
Coupon Rate	5.275%
Par Value	$ 125,000,000
Book Value	123,378,000	123,367,000
Fair Value	122,935,000
Term loan
Debt Instrument [Line Items]
Par Value	0
Less current maturity of term loan, par value	0
Book Value	0	86,875,000
Less current maturity of term loan, book value	0	$ 9,375,000
Fair Value	0
Less current maturity of term loan, fair value	$ 0

Long-Term And Short-Term Debt, Face Amount

No definition available.

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- Definition

Long-Term Debt, Fair Value, Excluding Current Maturities

+ References

No definition available.

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- Definition

Long-term Debt, Face Amount

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- Definition

Long-term Debt, Fair Value, Current Maturities

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Long-term debt, Face Amount, Current Maturities

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Long-term debt, Face Amount, Excluding Current Maturities

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Short-term debt, face amount

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No definition available.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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No definition available.

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

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