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Credit Facilities (Narrative) (Details) - USD ($) $ in Millions | 9 Months Ended |
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Sep. 30, 2019 | Dec. 31, 2018
Line of Credit Facility [Line Items] |  |
Total of committed credit facilities with banks | $ 575.0 |
Borrowings outstanding | 350.0 | $ 125.0
Stand-by letters of credit | 32.7 |
Wells Fargo Bank, N.A. Mature May 14, 2024 |  |
Line of Credit Facility [Line Items] |  |
Total of committed credit facilities with banks | $ 300.0 |
Committed credit facilities maturity | May 14, 2024 |
Borrowings outstanding | $ 75.0 |
Interest rate swap facility, amount | $ 75.0 |
Line of credit facility, interest rate | 2.72% |
Interest rate swap facility, fixed interest | 2.32% |
Interest rate swap facility, maturity date | May 14, 2024 |
BMO Harris Bank N.A. Mature May 14, 2024 |  |
Line of Credit Facility [Line Items] |  |
Total of committed credit facilities with banks | $ 200.0 |
Committed credit facilities maturity | May 14, 2024 |
Borrowings outstanding | $ 75.0 |
Interest rate swap facility, amount | $ 75.0 |
Line of credit facility, interest rate | 2.79% |
Interest rate swap facility, fixed interest | 2.36% |
Interest rate swap facility, maturity date | May 14, 2024 |
Mature July 13, 2020 |  |
Line of Credit Facility [Line Items] |  |
Total of committed credit facilities with banks | $ 75.0 |
Committed credit facilities maturity | Jul. 13, 2020 |
Additional Outstanding Debt Under Credit Facilities |  |
Line of Credit Facility [Line Items] |  |
Borrowings outstanding | $ 200.0 |
Line of credit facility, interest rate | 2.67% |

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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The effective interest rate at the end of the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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