Fair Value Of Financial Instruments (Schedule Of Changes In Fair Value Associated With Level 3 Financial Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers, Into Level 3		$ 0
Transfers, Out of Level 3		0
Non-Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1	1
Ending Balance	1	1
Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	355	357
Unrealized gains/(losses), Included in changes in net assets		3
Redemptions		(5)
Net change		(2)
Ending Balance	355	355
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	123	253
Unrealized gains/(losses), Included in changes in net assets		(130)
Realized gains/(losses)	(22)	(22)
Net change	(22)	(152)
Ending Balance	101	101
Equity Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	25,303	34,789
Unrealized gains/(losses), Included in changes in net assets	997	1,086
Redemptions	(9,775)	(19,350)
Net change	(8,778)	(18,264)
Ending Balance	16,525	16,525
Auction Rate Municipal Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	846	846
Unrealized gains/(losses), Included in changes in net assets	3	3
Redemptions	(50)	(50)
Net change	(47)	(47)
Ending Balance	799	799
Other Investment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	857	857
Ending Balance	$ 857	857
Fixed Income Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		242
Redemptions		(242)
Net change		$ (242)

Fair value measurement with unobservable inputs reconciliation recurring basis asset redemptions.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis realized asset gain loss included in earnings.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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- Definition

Amount of increase (decrease) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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