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Credit and Other Debt Agreements - Note Purchase Agreements - Additional Information (Detail) - USD ($) $ in Millions |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | ---
Aug. 04, 2017 | Aug. 02, 2017 | Jun. 27, 2017 | Jun. 13, 2017 | Dec. 31, 2017
Debt Instrument [Line Items] |  |  |  |  |
Realized a cash gain on hedging transaction |  |  |  |  | $ 8.3
Note Purchase Agreements [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Amount payable to redeem the notes, percent of the principal amount |  |  |  |  | 100.00%
Discount rate used to compute the remaining scheduled payments of principal and interest |  |  |  |  | U.S. Treasury yield plus 0.5%
Note Purchase Agreements [Member] | Floating Interest Rate 0.0% LIBOR Due October 25, 2017 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Quarterly payments of interest |  |  |  |  | $ 50.0
Quarterly payments of interest rate |  |  |  |  | 0.00%
Debt instrument, maturity date |  |  |  |  | Feb. 28, 2018
Quarterly payments of interest, description |  |  |  |  | Three-month LIBOR
Note Purchase Agreements [Member] | Senior Unsecured Notes [Member] | Private Placement [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold | $ 98.0 | $ 300.0 | $ 250.0 | $ 648.0 |
Note Purchase Agreements [Member] | Senior Fixed Rate Notes [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold |  |  |  |  | $ 598.0
Weighted average interest rate of notes |  |  |  |  | 4.04%
Note Purchase Agreements [Member] | Senior Fixed Rate Notes [Member] | Weighted Average [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Weighted average maturity of notes |  |  |  |  | 11 years 7 months 6 days
Note Purchase Agreements [Member] | 6.44% Senior Notes, Series B [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold |  |  |  |  | $ 300.0
Repayment of notes |  |  |  |  | $ 300.0
Debt instrument, maturity date |  |  |  |  | Aug. 03, 2017

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- Definition Amount Payable to Redeem the Notes, Percent of the Principal Amount + References No definition available. + Details
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- Definition Discount Rate used to Compute the Remaining Scheduled Payments of Principal and Interest + References No definition available. + Details
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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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- Definition The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR. + References No definition available. + 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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- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + 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)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 + Details
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- Definition The fair value of notes issued in noncash investing and financing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586 + Details
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