Supplementary Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 307,216	$ 308,616	$ 255,993	$ 263,852	$ 278,312	$ 278,315	$ 272,796	$ 273,501	$ 1,135,677	$ 1,102,924	$ 1,143,371
Operating Income	87,954	81,898	80,757	79,671	90,834	88,690	84,211	77,773	330,280	341,508	335,683
Net Income Including the Noncontrolling Interests in Subsidiaries	61,632	61,994	38,667	60,006	131,974	57,241	54,659	51,027	222,299	294,901	221,514
Amounts Attributable to Federated Investors, Inc.
Net income	$ 61,536	$ 59,608	$ 38,822	$ 60,331	$ 131,810	$ 56,439	$ 53,451	$ 49,641	$ 220,297	$ 291,341	$ 208,919
Earnings Per Common Share—Basic and Diluted (usd per share)	$ 0.61	$ 0.59	$ 0.38	$ 0.60	$ 1.31	$ 0.56	$ 0.53	$ 0.49	$ 2.18	$ 2.87	$ 2.03
Derivative, Loss on Derivative			$ 29,000
Reduction to income tax provision					$ 70,400					$ 70,400
Earnings per share impact of revaluation of net deferred tax liability (usd per share)					$ 0.70					$ 0.69