Document and Entity Information	9 Months Ended
Sep. 30, 2011	Oct. 26, 2011 Class A [Member]	Oct. 26, 2011 Class B [Member]
Entity Registrant Name	FEDERATED INVESTORS INC /PA/
Entity Central Index Key	0001056288
Trading Symbol	FII
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2011
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Amendment Flag	false
Entity Common Stock, Shares Outstanding		9,000	103,757,440

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