Fair Value Of Financial Instruments (Schedule Of Changes In Fair Value Carrying Values Associated With Level 3 Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Corporate Fixed Income Securities [Member]
Beginning Balance	$ 583
Unrealized gains/(losses), Included in changes in net assets	216
Purchases, Assets	7,494
Sales, Assets	(257)
Redemptions, Assets	(562)
Net change, Assets	6,891
Ending Balance, Assets	7,474
Equity Securities [Member]
Unrealized gains/(losses), Included in changes in net assets	1,168
Purchases, Assets	11,476
Sales, Assets	(110)
Net change, Assets	12,534
Ending Balance, Assets	12,534
State And Municipal Securities [Member]
Beginning Balance	90,487	[1]
Unrealized gains/(losses), Included in OCI, Assets	(235)	[1],[2]
Realized gains/(losses), Assets	6	[1],[3]
Purchases, Assets	5,000	[1]
Redemptions, Assets	(300)	[1]
Net change, Assets	4,471	[1]
Ending Balance, Assets	94,958	[1]
Equity Auction Rate Securities [Member]
Beginning Balance	64,397
Unrealized gains/(losses), Included in changes in net assets	304
Purchases, Assets	75
Redemptions, Assets	(1,375)
Net change, Assets	(996)
Ending Balance, Assets	63,401
Municipal Auction Rate Securities [Member]
Beginning Balance	14,067
Unrealized gains/(losses), Included in changes in net assets	32
Redemptions, Assets	(100)
Net change, Assets	(68)
Ending Balance, Assets	13,999
Other Investment [Member]
Beginning Balance	37,297
Unrealized gains/(losses), Included in changes in net assets	3,661
Realized gains/(losses), Assets	(208)	[3]
Purchases, Assets	42,925
Sales, Assets	(1,286)
Redemptions, Assets	(131)
Net change, Assets	44,961
Ending Balance, Assets	$ 82,258

[1] Included in available-for-sale securities owned in the consolidated statements of financial condition.

[2] Unrealized gains/(losses) related to available-for-sale securities are reported in accumulated other comprehensive loss in the consolidated statements of financial condition.

[3] Realized and unrealized gains/(losses) related to trading securities and investments are reported in other income in the consolidated statements of operations.