FAIR VALUE MEASUREMENT - Schedule of fair value hierarchy for assets measured at fair value on a recurring basis (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets:
Total assets	$ 176.5	$ 71.0
Liabilities:
Contingent consideration liabilities	20.5	2.2
Total liabilities	910.0	893.2
Level 1
Assets:
Total assets	176.5	71.0
Liabilities:
Total liabilities	20.9	23.4
Level 2
Liabilities:
Total liabilities	868.6	867.6
Level 3
Liabilities:
Contingent consideration liabilities	20.5	2.2
Total liabilities	20.5	2.2
Recurring
Assets:
Total assets	176.5	71.0
Liabilities:
Contingent consideration liabilities	20.5	2.2
Total liabilities	20.5	2.2
Recurring | U.S. Treasury securities
Assets:
Total assets	155.6	47.6
Recurring | Marketable securities | Mutual funds
Assets:
Total assets	13.1	15.7
Recurring | Marketable securities | Money market funds
Assets:
Total assets	7.8	7.7
Recurring | Level 1
Assets:
Total assets	176.5	71.0
Recurring | Level 1 | U.S. Treasury securities
Assets:
Total assets	155.6	47.6
Recurring | Level 1 | Marketable securities | Mutual funds
Assets:
Total assets	13.1	15.7
Recurring | Level 1 | Marketable securities | Money market funds
Assets:
Total assets	7.8	7.7
Recurring | Level 3
Liabilities:
Contingent consideration liabilities	20.5	2.2
Total liabilities	$ 20.5	$ 2.2