Management Contracts Purchased - Additional Information (Detail) (USD $)	0 Months Ended			3 Months Ended
	Oct. 28, 2013	Nov. 05, 2013	Oct. 26, 2012	Sep. 30, 2013	Mar. 31, 2015 Funds
Contracts In Progress Costs And Earnings [Line Items]
Number of mutual funds					13
Number of funds acquired			10
Acquisition of FBR & Co. (FBRC) deal			$ 2,200,000,000
Additional loan borrowed	16,300,000
Payments to acquire management contract rights through available cash	3,400,000
FBR Funds [Member]
Contracts In Progress Costs And Earnings [Line Items]
Initial payment based upon the net asset value of the FBR Funds			19,692,137
Contingent payment based upon the net asset value of the FBR Funds		19,193,595
Additional loan borrowed				13,286,666
Contingent payment due under the asset purchase agreement	$ 19,193,595