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Long-term Debt (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Instrument [Line Items] |  |
Long-term debt, gross | $ 196.1 | $ 196.7
Long-term debt | 195.5 | 196.1
Unamortized debt issuance costs | 0.6 | 0.6
Current portion of long-term debt | 0.0 | 0.1
Long-term debt, excluding current portion | 195.5 | 196.0
Notes payable, Due 2019 [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt, gross | 0.0 | $ 0.1
Revolving credit facility, Due 2020 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument, stated interest rate |  | 1.00%
Long-term debt, gross | $ 0.0 | $ 28.6
Revolving credit facility, Due 2024 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument, stated interest rate | 0.875% |
Long-term debt, gross | $ 28.1 |
Series A Notes, Due 2022 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument, stated interest rate | 3.67% | 3.67%
Long-term debt, gross | $ 42.0 | $ 42.0
Series B Notes, Due 2024 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument, stated interest rate | 3.82% | 3.82%
Long-term debt, gross | $ 53.0 | $ 53.0
Series C Notes, Due 2027 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument, stated interest rate | 4.02% | 4.02%
Long-term debt, gross | $ 73.0 | $ 73.0

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- Definition 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: 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=6879938&loc=d3e572229-122910 Reference 3: 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 4: 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 + Details
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