Value of input used to measure alternative investment.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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FAIR VALUE MEASUREMENTS - Fair value on a recurring basis (Details) $ in Millions	Dec. 31, 2022 USD ($) Y $ / shares	Dec. 31, 2021 USD ($)
Other long-term assets:
The company's recorded investment	$ 69.6	$ 85.6
Price Volatility Rate \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants	123.3
Discount yield \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants	4.1
Expected Term \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants \| Y	4.2
Exercise Price \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants \| $ / shares	1.068
Recurring basis
Other long-term assets:
Money market mutual funds		0.5
Investments measured at net asset value		12.4
Total assets at fair value	$ 21.7	12.9
Recurring basis \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Investments measured at net asset value	9.2
Recurring basis \| Hycroft
Other long-term assets:
The company's recorded investment	12.5
Recurring basis \| Quoted prices in active market (Level 1)
Other long-term assets:
Money market mutual funds		0.5
Total assets at fair value	12.5	$ 0.5
Recurring basis \| Quoted prices in active market (Level 1) \| Hycroft
Other long-term assets:
The company's recorded investment	12.5
Recurring basis \| Significant unobservable inputs (Level 3)
Other long-term assets:
Total assets at fair value	9.2
Recurring basis \| Significant unobservable inputs (Level 3) \| Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Investments measured at net asset value	$ 9.2