Share-Based Compensation (Compensation Expense and Unrecognized Compensation Costs) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.0
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.4
Weighted Average Remaining Recognition Period	1 year 8 months 12 days
Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.7
Weighted Average Remaining Recognition Period	1 year 8 months 12 days
Restricted Stock Units Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 1.6
Weighted Average Remaining Recognition Period	1 year 9 months 18 days
Cash Incentive Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 2.0
Weighted Average Remaining Recognition Period	1 year 7 months 6 days
Selling, General and Administrative Expenses \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 0.0	$ 0.1	$ 0.3
Net of tax	0.0	0.1	0.3
Selling, General and Administrative Expenses \| Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	2.5	2.3	1.9
Net of tax	1.9	1.8	1.5
Selling, General and Administrative Expenses \| Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3.9	3.4	1.5
Net of tax	3.0	2.6	1.2
Selling, General and Administrative Expenses \| Equity Classified Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	6.4	5.8	3.7
Net of tax	4.9	4.5	3.0
Selling, General and Administrative Expenses \| Restricted Stock Units Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	2.1	1.7	0.8
Net of tax	1.6	1.3	0.6
Selling, General and Administrative Expenses \| Cash Incentive Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	5.1	3.4	0.6
Net of tax	3.9	2.6	0.4
Selling, General and Administrative Expenses \| Liability Classified Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	7.2	5.1	1.4
Net of tax	$ 5.5	$ 3.9	$ 1.0

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, after tax, of expense for award under share-based payment arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sxc_RestrictedStockUnitsSettledinCashMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sxc_CashIncentiveAwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sxc_EquityClassifiedAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sxc_LiabilityClassifiedAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: