Related-Party Transactions (Expenses Incurred By Holdings From Services Provided By Affiliated Company) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Related-Party Transactions [Abstract]
Expenses incurred	$ 23,046	$ 20,289	$ 46,229	$ 41,459

Expenses incurred by holdings from services provided by affiliates

No definition available.

Name:	cik0000914748_ExpensesIncurredByHoldingsFromServicesProvidedByAffiliates
Namespace Prefix:	cik0000914748_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration