Supplemental Guarantor Information (Details)	Sep. 30, 2017 USD ($)
Supplemental Guarantor Information
Independent assets	$ 0
Independent operations	$ 0
Ownership interest in each of the subsidiary guarantors (as a percent)	100.00%

Represents the ownership interest in each of the subsidiary guarantors.

No definition available.

Name:	eva_OwnershipInterestInEachOfSubsidiaryGuarantors
Namespace Prefix:	eva_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant