FAIR VALUE MEASUREMENT - Fair Value Hierarchy for Assets and Liabilities on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Assets:
Note receivable - building sale	$ 6.4	$ 6.2
Total assets	214.0	116.5
Level 1
Assets:
Note receivable - building sale	0.0	0.0
Total assets	207.6	110.3
Level 2
Assets:
Note receivable - building sale	0.0	0.0
Total assets	0.0	0.0
Level 3
Assets:
Note receivable - building sale	6.4	6.2
Total assets	6.4	6.2
Fair Value, Recurring
Assets:
Note receivable - building sale	6.4	6.2
Total assets	214.0	116.5
Fair Value, Recurring | US Treasury Securities
Assets:
Debt securities	176.6	70.0
Fair Value, Recurring | Mutual funds
Assets:
Marketable securities	24.2	23.8
Fair Value, Recurring | Money market funds
Assets:
Marketable securities	6.8	16.5
Fair Value, Recurring | Level 1
Assets:
Note receivable - building sale	0.0	0.0
Total assets	207.6	110.3
Fair Value, Recurring | Level 1 | US Treasury Securities
Assets:
Debt securities	176.6	70.0
Fair Value, Recurring | Level 1 | Mutual funds
Assets:
Marketable securities	24.2	23.8
Fair Value, Recurring | Level 1 | Money market funds
Assets:
Marketable securities	6.8	16.5
Fair Value, Recurring | Level 2
Assets:
Note receivable - building sale	0.0	0.0
Total assets	0.0	0.0
Fair Value, Recurring | Level 2 | US Treasury Securities
Assets:
Debt securities	0.0	0.0
Fair Value, Recurring | Level 2 | Mutual funds
Assets:
Marketable securities	0.0	0.0
Fair Value, Recurring | Level 2 | Money market funds
Assets:
Marketable securities	0.0	0.0
Fair Value, Recurring | Level 3
Assets:
Note receivable - building sale	6.4	6.2
Total assets	6.4	6.2
Fair Value, Recurring | Level 3 | US Treasury Securities
Assets:
Debt securities	0.0	0.0
Fair Value, Recurring | Level 3 | Mutual funds
Assets:
Marketable securities	0.0	0.0
Fair Value, Recurring | Level 3 | Money market funds
Assets:
Marketable securities	$ 0.0	$ 0.0