Investments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 fund	Dec. 31, 2013 fund	Dec. 31, 2012
Investments [Abstract]
Net realized gains/losses transferred from accumulated other comprehensive income	$ 12,800,000	$ 3,200,000	$ 4,700,000
Number of affiliated funds holding seed money	146	149
Available-for-sale debt securities maturing in one to five years	3,000,000
Available-for-sale debt securities maturing in five to ten years	6,700,000
Charges to other comprehensive income from other-than-temporary impairment related to non-credit factors		0
Gains and losses on trading securities	12,300,000	33,800,000
Net Realized and Unrealized Gain (Loss) on Trading Securities	15,400,000	38,500,000	19,700,000
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage Ownership In Private Equity, Real Estate, and Other Entities	5.00%
Seed Money [Member]
Schedule of Available-for-sale Securities [Line Items]
Other-than-temporary impairment charges on seed money investments	$ 0	$ 0