Investment in Securities (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Trading securities:
Trading Securities, Cost	$ 190,204,000	$ 187,210,000	$ 190,204,000	$ 187,210,000	$ 196,968,000
Trading securities, fair value	201,533,000	181,134,000	201,533,000	181,134,000	203,146,000
Available for sale securities:
Available-for-sale Securities, Cost	16,036,000	18,085,000	16,036,000	18,085,000	17,849,000
Available for sale securities, Fair Value	33,912,000	33,625,000	33,912,000	33,625,000	35,187,000
Investment in Securities, Cost	206,240,000	205,295,000	206,240,000	205,295,000	214,817,000
Investments in securities	235,445,000	214,759,000	235,445,000	214,759,000	238,333,000
Trading Securities:
Proceeds			3,044,000	7,979,000	5,320,000
Fair Value	3,856,000	6,743,000	3,856,000	6,743,000	5,488,000
Net gain/(loss) on equity derivative	(411,000)	0	(425,000)	0
Shares under derivative contract (in shares)	1,100,000	0	1,100,000	0	142,000
Derivative fair value of derivative net	(6,000)	0	(6,000)	0	24,000
Investment in Securities [Member] \| Trading Securities [Member] \| Government obligations [Member]
Trading securities:
Trading Securities, Cost	28,731,000	18,698,000	28,731,000	18,698,000	42,124,000
Trading securities, fair value	28,742,000	18,699,000	28,742,000	18,699,000	42,126,000
Investment in Securities [Member] \| Trading Securities [Member] \| Common Stock [Member]
Trading securities:
Trading Securities, Cost	160,027,000	166,989,000	160,027,000	166,989,000	153,294,000
Trading securities, fair value	170,846,000	160,861,000	170,846,000	160,861,000	159,314,000
Trading Securities:
Proceeds			3,044,000	7,979,000	5,271,000
Fair Value	3,816,000	6,743,000	3,816,000	6,743,000	5,415,000
Investment in Securities [Member] \| Trading Securities [Member] \| Mutual Funds [Member]
Trading securities:
Trading Securities, Cost	1,064,000	1,081,000	1,064,000	1,081,000	1,084,000
Trading securities, fair value	1,461,000	1,178,000	1,461,000	1,178,000	1,307,000
Investment in Securities [Member] \| Trading Securities [Member] \| Other Investments [Member]
Trading securities:
Trading Securities, Cost	382,000	442,000	382,000	442,000	466,000
Trading securities, fair value	484,000	396,000	484,000	396,000	399,000
Trading Securities:
Proceeds			0	0	49,000
Fair Value	40,000	0	40,000	0	73,000
Investment in Securities [Member] \| Available-for-sale Securities [Member] \| Common Stock [Member]
Available for sale securities:
Available-for-sale Securities, Cost	14,931,000	16,724,000	14,931,000	16,724,000	16,487,000
Available for sale securities, Fair Value	32,239,000	31,903,000	32,239,000	31,903,000	33,282,000
Investment in Securities [Member] \| Available-for-sale Securities [Member] \| Mutual Funds [Member]
Available for sale securities:
Available-for-sale Securities, Cost	1,105,000	1,361,000	1,105,000	1,361,000	1,362,000
Available for sale securities, Fair Value	1,673,000	1,722,000	1,673,000	1,722,000	1,905,000
Investment in Sponsored Registered Investment Companies [Member] \| Trading Securities [Member] \| Mutual Funds [Member]
Trading securities:
Trading Securities, Cost	19,000	15,000	19,000	15,000	15,000
Trading securities, fair value	24,000	24,000	24,000	24,000	18,000
Investment in Sponsored Registered Investment Companies [Member] \| Available-for-sale Securities [Member] \| Mutual Funds [Member]
Available for sale securities:
Available-for-sale Securities, Cost	2,080,000	2,241,000	2,080,000	2,241,000	2,213,000
Available for sale securities, Fair Value	3,468,000	3,384,000	3,468,000	3,384,000	3,341,000
Investment in Sponsored Registered Investment Companies [Member] \| Available-for-sale Securities [Member] \| Closed end Funds [Member]
Available for sale securities:
Available-for-sale Securities, Cost	36,721,000	38,116,000	36,721,000	38,116,000	37,104,000
Available for sale securities, Fair Value	$ 60,731,000	$ 52,156,000	$ 60,731,000	$ 52,156,000	$ 55,855,000

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