MARKETABLE SECURITIES - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 577.2	$ 569.2
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	335.4	328.8
Fair Value, Inputs, Level 1 [Member] | Mutual Funds and Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	279.2	274.0
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	56.2	54.8
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	241.8	240.4
Fair Value, Inputs, Level 2 [Member] | U.S. Government Issued Debt Securities (Agency and Treasury) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	57.0	63.0
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	41.6	41.1
Fair Value, Inputs, Level 2 [Member] | Asset-Backed Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	19.8	18.5
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	112.5	107.5
Fair Value, Inputs, Level 2 [Member] | Other Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 10.9	$ 10.3