Related Party Transactions (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Related Party Transactions, Revenue [Abstract]
Advisory fee waiver, period			10 years
Affiliated Entity [Member]
Related Party Transactions, Revenue [Abstract]
Investment advisory and administrative fees	$ 41,001,000	$ 33,835,000	$ 113,847,000	$ 100,119,000
Distribution and service fees	2,881,000	2,457,000	8,129,000	7,458,000
Total	43,882,000	36,292,000	121,976,000	107,577,000
Advisory fees waived	0	381,000	299,000	1,462,000
Fund expenses, included in general and administrative expenses	1,214,000	1,779,000	4,735,000	5,092,000
Receivables, company sponsored mutual funds	$ 17,190,000		$ 17,190,000		$ 12,947,000