MARKETABLE SECURITIES - Schedule of Contractual Maturities (Details) $ in Millions	Sep. 30, 2017 USD ($)
Amortized Cost
Less than one year	$ 40.2
One to five years	56.7
Six to ten years	52.6
Greater than ten years	137.0
Total Debt Securities	286.5
Fair Value
Less than one year	40.2
One to five years	57.6
Six to ten years	54.1
Greater than ten years	139.6
Total Debt Securities	$ 291.5