FAIR VALUE MEASUREMENTS - Schedule of fair value hierarchy for assets measured at fair value on a recurring basis (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets:
Money market funds	$ 140.0	$ 143.5
Total assets	524.0	425.3
Liabilities:
Contingent consideration liabilities	2.2	56.6
Total liabilities	1,417.3	1,443.3
Money market funds
Assets:
Money market funds	2.5	2.5
Level 1
Assets:
Money market funds	140.0	143.5
Total assets	524.0	425.3
Level 2
Liabilities:
Total liabilities	1,415.1	1,386.7
Level 3
Liabilities:
Contingent consideration liabilities	2.2	56.6
Total liabilities	2.2	56.6
Recurring
Assets:
Total assets	134.3	49.8
Liabilities:
Contingent consideration liabilities	2.2	56.6
Total liabilities	2.2	56.6
Recurring | Money market funds
Assets:
Money market funds	2.5	2.5
Recurring | U.S. Treasury securities
Assets:
Total assets	131.8	47.3
Recurring | Level 1
Assets:
Total assets	134.3	49.8
Recurring | Level 1 | Money market funds
Assets:
Money market funds	2.5	2.5
Recurring | Level 1 | U.S. Treasury securities
Assets:
Total assets	131.8	47.3
Recurring | Level 3
Liabilities:
Contingent consideration liabilities	2.2	56.6
Total liabilities	$ 2.2	$ 56.6