Earnings Per Share Attributable to Federated Investors, Inc. Shareholders Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Thousands, except Per Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Net income attributable to Federated Investors, Inc.	$ 38,320		$ 43,056		$ 113,964		$ 132,713
Net income attributable to Federated Common Stock - Basic and Diluted	$ 0.37	[1]	$ 0.42	[1]	$ 1.09	[1]	$ 1.27	[1]
Basic [Member]
Net income attributable to Federated Investors, Inc.	38,320		43,056		113,964		132,713
Less: Total income available to participating unvested restricted shareholders	(1,211)	[2]	(1,251)	[2]	(3,746)	[2]	(5,766)	[2]
Total net income attributable to Federated Common Stock	37,109	[1]	41,805	[1]	110,218	[1]	126,947	[1]
Diluted [Member]
Net income attributable to Federated Investors, Inc.	38,320		43,056		113,964		132,713
Less: Total income available to participating unvested restricted shareholders	(1,211)		(1,251)		(3,746)		(5,766)
Total net income attributable to Federated Common Stock	$ 37,109		$ 41,805		$ 110,218		$ 126,947
Denominator [Member]
Basic weighted-average common shares outstanding	100,684		99,916		100,725		99,907
Dilutive potential shares from stock options	0		38		31		84
Diluted weighted-average common shares outstanding	100,684		99,954		100,756		99,991

[1] Federated Common Stock excludes unvested restricted stock which are deemed participating securities in accordance with the two-class method of computing earnings per share.

[2] Income available to participating restricted shareholders includes dividends paid to unvested restricted shareholders, net of forfeited dividends, and their proportionate share of undistributed earnings, if any.