Retirement Benefits Plans (Details Textual) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Defined contribution plan matching contribution	$ 1.6	$ 1.6

Defined contribution plan employer matching contribution amount.

No definition available.

Name:	sxc_DefinedContributionPlanEmployerMatchingContributionAmount
Namespace Prefix:	sxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration