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Long-Term Debt - Derivative Instruments and Hedging Activities Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
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Mar. 09, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Derivatives, Fair Value [Line Items] |  |  |  |
Cash premiums paid |  | $ 2.8 | $ 1.9 |
Unamortized premium |  | 4.6 | 1.9 |
Incremental interest expense |  | 0.2 | 3.1 | $ 5.5
Net benefit expected to be reclassified |  | 2.9 |  |
Designated as hedging instrument | Cash flow swaps and interest rate caps |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Net cash proceeds | $ 4.8 |  |  |
Derivative asset, fair value of interest rate swap and cap positions |  | 4.8 |  |
Designated as hedging instrument | Interest rate swap |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative liability, fair value of interest rate swap and cap positions |  |  | 4.7 |
Designated as hedging instrument | Other current assets | Cash flow swaps and interest rate caps |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative asset, fair value of interest rate swap and cap positions |  | 1.8 |  |
Designated as hedging instrument | Other current assets | Interest rate swap |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative liability, fair value of interest rate swap and cap positions |  |  | 0.9 |
Designated as hedging instrument | Other assets | Cash flow swaps and interest rate caps |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative asset, fair value of interest rate swap and cap positions |  | $ 3.0 |  |
Designated as hedging instrument | Other assets | Interest rate swap |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative asset, fair value of interest rate swap and cap positions |  |  | 5.1 |
Designated as hedging instrument | Other accrued liabilities | Interest rate swap |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative liability, fair value of interest rate swap and cap positions |  |  | 1.0 |
Designated as hedging instrument | Other long-term liabilities | Interest rate swap |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Derivative liability, fair value of interest rate swap and cap positions |  |  | $ 0.3 |

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- Definition Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4D -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959 + Details
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