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MARKETABLE SECURITIES - Fair Value Measurement (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | $ 473.6 | $ 470.2
Level 1 |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 285.5 | 287.2
Level 1 | Mutual Funds and Equities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 254.2 | 246.0
Level 1 | Money Market Funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 31.3 | 41.2
Level 2 |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 188.1 | 183.0
Level 2 | U.S. Government Issued Debt Securities (Agency and Treasury) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 81.3 | 72.9
Level 2 | Corporate Debt Securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 65.3 | 63.8
Level 2 | Asset-Backed Debt Securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 12.6 | 11.9
Level 2 | Municipal Bonds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | 12.3 | 24.0
Level 2 | Other Fixed Income Securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total Marketable Securities | $ 16.6 | $ 10.4

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