LEASES - Lease Cost and Other Information (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
LEASES.
Operating lease costs	$ 3.4	$ 8.8
Weighted average remaining lease term (years)	9 years 4 months 24 days	9 years 4 months 24 days
Weighted average discount rate	3.50%	3.50%
Cash paid for amounts included in the measurement of lease liabilities		$ 7.5
Right-of-use assets obtained in exchange for lease liabilities		$ 21.0