LEASES - Lease Costs and Other Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jan. 01, 2019
Leases
Operating lease costs	$ 4.7	$ 3.4	$ 14.5	$ 8.8
Weighted average remaining lease term (years)	12 years 7 months 6 days	9 years 4 months 24 days	12 years 7 months 6 days	9 years 4 months 24 days
Weighted average discount rate	3.40%	3.50%	3.40%	3.50%
Cash paid for amounts included in the measurement of lease liabilities	$ 3.2	$ 2.7	$ 8.6	$ 7.5
Lease incentive for leasehold improvements			25.2
Right-of-use assets obtained in exchange for lease liabilities	0.9	$ 2.0	71.8	$ 21.0
Operating lease right of use assets	116.1		116.1		$ 53.4
Operating lease liabilities recognized upon adoption	$ 147.6		$ 147.6		$ 55.4
ASU 2016-02 | Restatement Adjustment
Leases
Operating lease right of use assets						$ 40.3
Operating lease liabilities recognized upon adoption						$ 42.8