FAIR VALUE MEASUREMENTS - Fair value on a recurring basis (Details) $ in Millions	Mar. 31, 2022 USD ($) Y $ / shares	Dec. 31, 2021 USD ($)
Other long-term assets:
The company's recorded investment	$ 79.1	$ 85.6
Price Volatility Rate | Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants	75.0
Discount yield | Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants	2.4
Expected Term | Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Estimates to value Warrants | Y	5
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	$ 2.0
Investments measured at net asset value	9.8
Total assets at fair value	118.7
Recurring basis | Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Investments measured at net asset value	38.0
Recurring basis | NCM
Other long-term assets:
The company's recorded investment	15.1
Recurring basis | Hycroft
Other long-term assets:
The company's recorded investment	53.8
Recurring basis | Quoted prices in active market (Level 1)
Other long-term assets:
Money market mutual funds	2.0
Total assets at fair value	70.9
Recurring basis | Quoted prices in active market (Level 1) | NCM
Other long-term assets:
The company's recorded investment	15.1
Recurring basis | Quoted prices in active market (Level 1) | Hycroft
Other long-term assets:
The company's recorded investment	53.8
Recurring basis | Significant unobservable inputs (Level 3)
Other long-term assets:
Total assets at fair value	38.0
Recurring basis | Significant unobservable inputs (Level 3) | Investment in Hycroft Mining Holding Corporation Warrants
Other long-term assets:
Investments measured at net asset value	$ 38.0