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Fair Value Of Financial Instruments (Schedule Of Changes In Fair Value Associated With Level 3 Financial Instruments) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Transfers, Into Level 3 | $ 0 |
Transfers, Out of Level 3 | (18,300) |
Non-Agency [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 1,082 | $ 1,476
Unrealized gains/(losses), Included in changes in net assets | (260) | (18)
Realized gains/(losses) | 90 | 54
Sales | (324) |
Redemptions | (230) | (430)
Net change | (724) | (394)
Ending Balance | 358 | 1,082
Corporate Equity Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 3,833 | 2,942
Unrealized gains/(losses), Included in changes in net assets | (133) | (361)
Realized gains/(losses) | 13 | 2,453
Purchases |  | 3,593
Sales | (120) |
Redemptions |  | (4,794)
Transfers, Out of Level 3 | (3,593) |
Net change | (3,833) | 891
Ending Balance |  | 3,833
Corporate Fixed Income Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 273 |
Purchases |  | 292
Redemptions | (31) | (19)
Net change | (31) | 273
Ending Balance | 242 | 273
Equity Auction Rate Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 48,689 | 50,442
Unrealized gains/(losses), Included in changes in net assets | 785 | 547
Purchases |  | 50
Redemptions |  | (2,350)
Transfers, Out of Level 3 | (14,685) |
Net change | (13,900) | (1,753)
Ending Balance | 34,789 | 48,689
Equity Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 600 | 619
Unrealized gains/(losses), Included in changes in net assets | (88) | (279)
Realized gains/(losses) | (259) |
Purchases |  | 253
Transfers, Into Level 3 |  | 7
Net change | (347) | (19)
Ending Balance | 253 | 600
Auction Rate Municipal Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 832 | 1,315
Unrealized gains/(losses), Included in changes in net assets | 14 | 67
Redemptions |  | (550)
Net change | 14 | (483)
Ending Balance | 846 | 832
Other Investment [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 1,240 | 20
Realized gains/(losses) | (383) |
Purchases |  | 3,782
Transfers, Into Level 3 |  | 465
Transfers, Out of Level 3 |  | (3,027)
Net change | (383) | 1,220
Ending Balance | $ 857 | $ 1,240

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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