Leases (Schedule of Future Minimum Sublease Rentals for Capital Leases) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Leases [Abstract]
2018	$ 3,699
2019	3,699
2020	2,157
2021	0
2022	0
Thereafter	0
Total	$ 9,555

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling Twelve Months

No definition available.

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingTwelveMonths
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling Year Five

+ References

No definition available.

+ Details

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingYearFive
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling Year Four

+ References

No definition available.

+ Details

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingYearFour
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling Year Three

+ References

No definition available.

+ Details

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingYearThree
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling Year Two

+ References

No definition available.

+ Details

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingYearTwo
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Capital Leases, Future Minimum Sublease Rentals, Due in Rolling after Year Five

+ References

No definition available.

+ Details

Name:	ceix_CapitalLeasesFutureMinimumSubleaseRentalsDueinRollingafterYearFive
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum payments receivable in the future under noncancelable subleases.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

+ Details

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

- References

No definition available.

+ Details

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