MARKETABLE SECURITIES - Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Less than one year	$ 59.2
One to five years	40.5
Six to ten years	33.6
Greater than ten years	95.1
Amortized Cost	228.4	$ 190.0
Fair Value
Less than one year	59.3
One to five years	41.4
Six to ten years	34.8
Greater than ten years	98.6
Total Debt Securities	$ 234.1	$ 186.4