Marketable Securities (Narrative) (Details) (USD $)	9 Months Ended		12 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 SEI Private Trust Company [Member] Minimum [Member]	Sep. 30, 2013 SEI Private Trust Company [Member] Maximum [Member]	Sep. 30, 2013 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2012 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2013 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2012 U.S. Government Agency And Commercial Paper Securities [Member]	Sep. 30, 2012 SIV Securities [Member]	Sep. 30, 2013 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2012 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2013 LSV-Sponsored Mutual Funds [Member]	Sep. 30, 2012 LSV-Sponsored Mutual Funds [Member]	Dec. 31, 2012 LSV-Sponsored Mutual Funds [Member]
Schedule of Investments [Line Items]
Net unrealized holding gains	$ 1,656,000		$ 2,829,000
Unrealized holding gains during the period, income tax expense	691,000		1,554,000
Available-for-sale Securities, Gross Realized Gains	710,000	0
Available-for-sale Securities, Gross Realized Losses	(261,000)	0
Available-for-sale Securities, Debt Maturities, Date				Dec. 15, 2020	Mar. 20, 2043
Trading securities	4,841,000		5,909,000								4,841,000		4,841,000		4,706,000
Trading Securities, Realized Gain (Loss)										7,343,000	610,000	357,000	135,000	520,000
Securities owned	20,728,000		20,088,000
Realized Investment Gains (Losses)						$ 0	$ 0	$ 0	$ 0