MARKETABLE SECURITIES - Contractual Maturities of Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Less than one year	$ 30.9
One to five years	65.5
Six to ten years	41.8
Greater than ten years	79.3
Amortized Cost	217.5	$ 213.1
Fair Value
Less than one year	30.9
One to five years	67.1
Six to ten years	43.9
Greater than ten years	83.4
Fair Value	$ 225.3	$ 224.2

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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