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, 2019	Dec. 31, 2018
Non-Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1	$ 1
Realized gains/(losses)	(1)
Net change	(1)
Ending Balance		1
Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	175	357
Unrealized gains/(losses), Included in changes in net assets	2	(164)
Redemptions	(2)	(18)
Net change		(182)
Ending Balance	175	175
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Realized gains/(losses)	452
Purchases	24,316
Sales	(16,081)
Redemptions	(1)
Transfers, Into Level 3	465
Net change	9,151
Ending Balance	9,151
Corporate Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers, Into Level 3	1,060
Net change	1,060
Ending Balance	1,060
Equity Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	16,632	34,789
Unrealized gains/(losses), Included in changes in net assets	261	1,193
Redemptions	(2,650)	(19,350)
Net change	(2,389)	(18,157)
Ending Balance	14,243	16,632
Auction Rate Municipal Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	704	846
Unrealized gains/(losses), Included in changes in net assets		8
Redemptions	(50)	(150)
Transfers, Out of Level 3	(470)
Net change	(520)	(142)
Ending Balance	184	704
Other Investment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	857	857
Redemptions	(4)
Net change	(4)
Ending Balance	$ 853	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)
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		253
Unrealized gains/(losses), Included in changes in net assets		(130)
Realized gains/(losses)		21
Sales		(144)
Net change		$ (253)