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, 2021	Dec. 31, 2020
Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 9
Unrealized gains/(losses)		(3,002)
Realized gains/(losses)		9,485
Purchases		68,104
Redemptions		16,750
Transfers into Level 3		6,930
Transfers out of Level 3		70
Net change		64,697
Ending Balance		64,706	$ 9
Corporate Equity Securities Financial Instruments Owned [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers into Level 3		225
Net change		225
Ending Balance		225
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		11,275
Unrealized gains/(losses)		(68)
Purchases		23,600
Sales		7,725
Transfers out of Level 3		225
Net change		15,582
Ending Balance		26,857	11,275
Other Financial Instrument Owned [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	[1]	11,284	9,326
Unrealized gains/(losses)	[1]		(3,126)
Realized gains/(losses)	[1]		(71)
Purchases	[1]		25,852
Sales	[1]		20,000
Redemptions	[1]		697
Net change	[1]		1,958
Ending Balance	[1]		11,284
Corporate Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance			1,060
Unrealized gains/(losses)		(1,000)
Purchases		3,000
Sales		2,000
Transfers into Level 3		5,754
Transfers out of Level 3			(1,060)
Net change		5,754	(1,060)
Ending Balance		5,754
Equity Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		12,933	14,427
Unrealized gains/(losses)		124	(1,494)
Redemptions		25
Net change		99	(1,494)
Ending Balance		13,032	12,933
Other Investment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		42,113	853
Unrealized gains/(losses)		654	(296)
Sales			(20)
Transfers into Level 3			41,576
Transfers out of Level 3		6,930
Net change		(6,276)	41,260
Ending Balance		$ 35,837	$ 42,113

[1] Includes asset-backed securities and loans.