Employee Benefit Plans (Incurred Expenses Related To Defined Contribution Plans For Non-U.S. Employees) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Benefit Plans [Abstract]
Incurred expenses	$ 514	$ 494	$ 447

Expenses Incurred Under Defined Contribution Plans For Non-US Employees

No definition available.

Name:	cik0000914748_ExpensesIncurredUnderDefinedContributionPlansForNonUsEmployees
Namespace Prefix:	cik0000914748_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration