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Derivative Instruments - Interest rate swap agreement (Details) $ in Millions | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2020 USD ($) agreement | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) agreement | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) agreement | Dec. 31, 2016 agreement
Interest rate contract |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Borrowings at variable interest rates | $ 559.7 |  | $ 559.7 |  | $ 404.3 |
Number of interest rate swap agreements | agreement | 2 |  | 2 |  | 1 | 1
Derivative, notional amount | $ 100.0 |  | $ 100.0 |  | $ 100.0 |
Net fair value of swap liability | 5.4 |  | 5.4 |  | $ 1.7 |
Gain (loss) recorded to net finance costs | $ (0.6) | $ 0.2 | $ (0.6) | $ 0.4 |  |
2016 swap agreement |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Remaining maturity term |  |  | 10 months |  |  |
2019 swap agreement |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Remaining maturity term |  |  | 48 months |  |  |

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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 Period remaining until the derivative contract matures, 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 The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time. + References No definition available. + Details
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