FAIR VALUE MEASUREMENT - Schedule of fair value hierarchy for assets measured at fair value on a recurring basis (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets:
Total assets	$ 43.6	$ 71.0
Liabilities:
Contingent consideration liabilities	17.5	2.2
Total liabilities	904.0	893.2
Level 1
Assets:
Total assets	43.6	71.0
Liabilities:
Total liabilities	18.4	23.4
Level 2
Liabilities:
Total liabilities	868.1	867.6
Level 3
Liabilities:
Contingent consideration liabilities	17.5	2.2
Total liabilities	17.5	2.2
Recurring
Assets:
Total assets	43.6	71.0
Liabilities:
Contingent consideration liabilities	17.5	2.2
Total liabilities	17.5	2.2
Recurring | U.S. Treasury securities
Assets:
Total assets	25.2	47.6
Recurring | Marketable securities | Mutual funds
Assets:
Total assets	11.8	15.7
Recurring | Marketable securities | Money market funds
Assets:
Total assets	6.6	7.7
Recurring | Level 1
Assets:
Total assets	43.6	71.0
Recurring | Level 1 | U.S. Treasury securities
Assets:
Total assets	25.2	47.6
Recurring | Level 1 | Marketable securities | Mutual funds
Assets:
Total assets	11.8	15.7
Recurring | Level 1 | Marketable securities | Money market funds
Assets:
Total assets	6.6	7.7
Recurring | Level 3
Liabilities:
Contingent consideration liabilities	17.5	2.2
Total liabilities	$ 17.5	$ 2.2