Fair Value Of Financial Instruments (Schedule Of Changes In Fair Value Associated With Level 3 Financial Instruments) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 64,706
Unrealized gains/(losses)	4,750
Realized gains	1,673
Redemptions	17,713
Net change	(11,290)
Ending Balance	53,416
Corporate Equity Securities Financial Instruments Owned Member
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	225
Unrealized gains/(losses)	839
Realized gains	336
Sales	(387)
Net change	788
Ending Balance	1,013
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	26,857
Unrealized gains/(losses)	60
Realized gains	325
Purchases	33,222
Sales	(24,900)
Redemptions	604
Net change	8,103
Ending Balance	34,960
Corporate Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	5,754
Unrealized gains/(losses)	6,124
Net change	6,124
Ending Balance	11,878
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	13,032
Unrealized gains/(losses)	711
Net change	711
Ending Balance	13,743
Other Investment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	35,837
Unrealized gains/(losses)	(1,066)
Realized gains	992
Sales	(999)
Redemptions	39
Net change	(1,112)
Ending Balance	$ 34,725