Leases (Tables)

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Components of Lease Expense

The components of lease expense for the periods presented below were as follows:

	Year Ended December 31,
	2022		2021		2020
	(Dollars in millions)
Operating lease cost:
Operating leases	$	18.9	$	19.8	$	28.8
Short-term leases	30.6		15.5		39.1
Variable leases	7.6		2.7		4.6
Sublease income	(1.3)		(1.9)		(2.3)
Total operating lease cost	$	55.8	$	36.1	$	70.2
Finance lease cost:
Amortization of right-of-use assets	$	6.3	$	5.9	$	3.5
Interest on lease liabilities	2.1		2.7		0.8
Total finance lease cost	$	8.4	$	8.6	$	4.3

Schedule of Supplemental Balance Sheet Information Related to Leases

Supplemental balance sheet information related to leases at December 31, 2022 and 2021 was as follows:

	December 31,
	2022			2021
	(Dollars in millions)
Operating leases:
Operating lease right-of-use assets	$	26.9		$	35.5
Accounts payable and accrued expenses	$	16.8		$	16.4
Operating lease liabilities, less current portion	11.0			27.2
Total operating lease liabilities	$	27.8		$	43.6
Finance leases:
Property, plant, equipment and mine development	$	36.1		$	32.2
Accumulated depreciation	(12.6)			(7.4)
Property, plant, equipment and mine development, net	$	23.5		$	24.8
Current portion of long-term debt	$	13.2		$	15.3
Long-term debt, less current portion	10.4			14.0
Total finance lease liabilities	$	23.6		$	29.3
Weighted average remaining lease term (years)
Operating leases	2.0
Finance leases	6.7
Weighted average discount rate
Operating leases	5.7		%
Finance leases	7.2		%

Schedule of Supplemental Cash Flow Information Related to Leases

Supplemental cash flow information related to leases for the periods presented below was as follows:

	Year Ended December 31,
	2022		2021		2020
	(Dollars in millions)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$	20.5	$	24.3	$	35.1
Operating cash flows for finance leases	2.1		3.8		0.8
Financing cash flows for finance leases	9.3		8.2		8.9
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	13.5		7.1		16.5
Finance leases	6.4		24.4		1.6

Lessee, Operating Lease, Liability, Maturity

The Company's leases have remaining lease terms ranging from 1 year to 8.3 years, and may include options to extend the terms, as applicable. The contractual maturities of lease liabilities were as follows:

Period Ending December 31,	Operating Leases		Finance Leases
	(Dollars in millions)
2023	$	18.6	$	14.4
2024	7.4		5.7
2025	1.6		4.0
2026	1.4		2.2
2027	0.3		1.0
2028 and thereafter	0.4		—
Total lease payments	29.7		27.3
Less imputed interest	(1.9)		(3.7)
Total lease liabilities	$	27.8	$	23.6

Finance Lease, Liability, Maturity

The Company's leases have remaining lease terms ranging from 1 year to 8.3 years, and may include options to extend the terms, as applicable. The contractual maturities of lease liabilities were as follows:

Period Ending December 31,	Operating Leases		Finance Leases
	(Dollars in millions)
2023	$	18.6	$	14.4
2024	7.4		5.7
2025	1.6		4.0
2026	1.4		2.2
2027	0.3		1.0
2028 and thereafter	0.4		—
Total lease payments	29.7		27.3
Less imputed interest	(1.9)		(3.7)
Total lease liabilities	$	27.8	$	23.6