Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2020	Nov. 03, 2020
Statutory Accounting Practices
Restricted Cash Current Customer Deposits	$ 1.1	$ 1.1
Mineral rights	215.6	239.4
Deferred finance costs, net	1.0	1.6
Deferred finance costs, current	0.6	0.6
Final contribution to the plan	3.2
Debt instrument, face amount			$ 155.3
Interest rate			5.25%
Convertible Notes
Statutory Accounting Practices
Debt instrument, face amount				$ 155.3
Interest rate				5.25%
Cash on convertible notes	58.4	208.1
Principal amount of convertible notes	$ 13.2	$ 142.1
Paid-in Capital
Statutory Accounting Practices
Cash on convertible notes			$ 39.2
Retained Earnings
Statutory Accounting Practices
Cash on convertible notes			$ 6.7
ASU 2020-06
Statutory Accounting Practices
Diluted earnings per share		$ 65.28
Diluted earnings per share, decrease		$ 1.40
Minimum
Statutory Accounting Practices
Operating lease, remaining lease terms	1 year
Maximum
Statutory Accounting Practices
Operating lease, remaining lease terms	3 years
Exploration and production equipment | Minimum
Statutory Accounting Practices
Estimated useful life	1 year
Exploration and production equipment | Maximum
Statutory Accounting Practices
Estimated useful life	16 years
Building and building improvements | Minimum
Statutory Accounting Practices
Estimated useful life	5 years
Building and building improvements | Maximum
Statutory Accounting Practices
Estimated useful life	20 years
Mining properties and mineral rights | Minimum
Statutory Accounting Practices
Operating lease, remaining lease terms	10 years
Mining properties and mineral rights | Maximum
Statutory Accounting Practices
Operating lease, remaining lease terms	50 years