Fair Value of Financial Instruments (Schedule of Changes in Fair Value Carrying Values Associated With Level 3 Financial Instruments) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011		Sep. 30, 2011		Mar. 31, 2011
Corporate Fixed Income Securities [Member]
Unrealized gains/(losses), Included in OCI, Assets	$ 0	[1],[2]	$ 0	[1],[2]
Transfers, Into Level 3, Assets	0	[1]	0	[1]
Ending Balance, Assets	1,201	[1]	1,201	[1]
Beginning Balance, Liabilities			4,685		2,435
Unrealized gains/(losses), Included in changes in net liabilities		[3]	0	[3]
Unrealized gains/(losses), Included in OCI, Liabilities		[2]	0	[2]
Realized gains/(losses), Liabilities	(16)	[3]	(52)	[3]
Purchases, Liabilities			6,663
Sales, Liabilities	(2,419)		(11,296)
Redemptions, Liabilities			0
Transfers, Into Level 3, Liabilities			0
Transfers, Out of Level 3, Liabilities			0
Net change, Liabilities	(2,435)		(4,685)
Liabilities, Ending Balance					2,435
State and Municipal Securities [Member]
Beginning Balance			11,436		44,678
Unrealized gains/(losses), Included in changes in net assets	0	[3]	0	[3]
Unrealized gains/(losses), Included in OCI, Assets	316	[2]	2,403	[2]
Realized gains/(losses), Assets	43	[3]	858	[3]
Purchases, Assets	21,987		48,974
Sales, Assets	(24,126)		(24,126)
Redemptions, Assets	(400)		(775)
Transfers, Into Level 3, Assets	0		27,854
Transfers, Out of Level 3, Assets	0		0
Net change, Assets	21,946		55,188
Ending Balance, Assets	66,624		66,624		44,678
Auction Rate Securities [Member]
Beginning Balance			76,826		66,616
Unrealized gains/(losses), Included in changes in net assets	162	[3]	452	[3]
Unrealized gains/(losses), Included in OCI, Assets	0	[2]	0	[2]
Realized gains/(losses), Assets	0	[3]	0	[3]
Purchases, Assets	1,650		3,725
Sales, Assets	0		0
Redemptions, Assets	(4,225)		(16,800)
Transfers, Into Level 3, Assets	0		0
Transfers, Out of Level 3, Assets	0		0
Net change, Assets	(2,413)		(12,623)
Ending Balance, Assets	64,203		64,203		66,616
Municipal Auction Rate Securities [Member]
Beginning Balance			6,533		7,117
Unrealized gains/(losses), Included in changes in net assets	52	[3]	(44)	[3]
Unrealized gains/(losses), Included in OCI, Assets	0	[2]	0	[2]
Realized gains/(losses), Assets	0	[3]	0	[3]
Purchases, Assets	0		4,105
Sales, Assets	(125)		(2,900)
Redemptions, Assets	0		(650)
Transfers, Into Level 3, Assets	0		0
Transfers, Out of Level 3, Assets	0		0
Net change, Assets	(73)		511
Ending Balance, Assets	7,044		7,044		7,117
Other [Member]
Beginning Balance			38,502		38,958
Unrealized gains/(losses), Included in changes in net assets	(692)	[3]	2,872	[3]
Unrealized gains/(losses), Included in OCI, Assets	0	[2]	0	[2]
Realized gains/(losses), Assets	(94)	[3]	(681)	[3]
Purchases, Assets	170		994
Sales, Assets	0		0
Redemptions, Assets	(739)		(4,324)
Transfers, Into Level 3, Assets	240		240
Transfers, Out of Level 3, Assets	0		0
Net change, Assets	(1,355)
Ending Balance, Assets	37,603		37,603		38,958
Net change, Liabilities			$ (899)

[1] Included in trading securities owned in the consolidated statements of financial condition.

[2] Unrealized gains related to available-for-sale securities are reported in accumulated other comprehensive income 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.