Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended	3 Months Ended				9 Months Ended					3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 SEI Private Trust Company [Member] Minimum [Member]	Sep. 30, 2012 SEI Private Trust Company [Member] Maximum [Member]	Sep. 30, 2012 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2011 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2012 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2011 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2012 SIV Securities [Member]	Sep. 30, 2011 SIV Securities [Member]	Sep. 30, 2011 Stanfield Victoria SIV [Member]	Sep. 30, 2012 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2011 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2012 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2011 LSV-Sponsored Mutual Funds [Member]
Schedule of Investments [Line Items]
Net unrealized holding gains	$ 3,189		$ 2,574
Unrealized holding gains during the period, income tax expense	1,806		1,518
Available-for-sale Securities, Gross Realized Gain (Loss)	0	0
Available-for-sale Securities, Debt Maturities, Date				Dec. 15, 2020	Nov. 15, 2041
Net gains from SIV securities										7,343	4,128
Gains from cash payments received from SIV securities										6,201	8,430
Gains or losses from increase/decrease in fair value of SIV securities										1,142	(4,302)
Trading Securities, Realized Gain (Loss)												0	0	0	0	0
Securities owned	21,081		20,949
Realized Investment Gains (Losses)						$ 0	$ 0	$ 0	$ 0