LEASES - Lease Costs and Other Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 01, 2019
Leases
Operating lease costs	$ 5.0	$ 3.2	$ 9.8	$ 6.8
Weighted average remaining lease term (years)	12 years 9 months 18 days	9 years 6 months	12 years 9 months 18 days	9 years 6 months
Weighted average discount rate	3.40%	3.50%	3.40%	3.50%
Cash paid for amounts included in the measurement of lease liabilities	$ 2.6	$ 2.7	$ 5.4	$ 4.8
Lease incentive for leasehold improvements	4.8		25.2
Right-of-use assets obtained in exchange for lease liabilities	6.7	$ 0.1	70.9	$ 19.0
Operating lease right of use assets	117.8		117.8		$ 53.4
Operating lease liabilities recognized upon adoption	$ 148.0		$ 148.0		$ 55.4
ASU 2016-02 | Restatement Adjustment
Leases
Operating lease right of use assets						$ 40.3
Operating lease liabilities recognized upon adoption						$ 42.8