Related-Party Transactions (Dividends Received On Preferred Shares) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Dividends From Preferred Shares Of Affiliate [Member]
Related Party Transaction [Line Items]
Dividends received on preferred stock of affiliate	$ 7,758	$ 7,758

Dividends received on common shares, reported as net investment income in consolidated statements of operations and comprehensive income (loss).

No definition available.

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