Business Combination - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			6 Months Ended
	Jun. 01, 2017	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Purchase price, cash					$ 471,400
Goodwill			$ 171,170		171,170		$ 6,788
Other operating expenses			20,236	$ 12,457	33,462	$ 23,222
RidgeWorth
Business Acquisition [Line Items]
Purchase price	$ 547,100
Purchase price, cash	$ 471,400
Purchase price, shares issued (in shares)	213,669
Purchase price, shares issued, value	$ 21,700
Purchase price, price of shares issued (in dollars per share)	$ 101.76
Purchase price, contingent consideration	$ 51,700
Purchase price, deferred cash payments	2,300
Goodwill	164,382
Tax deductible goodwill			123,000		123,000
Transaction and integration costs			16,300
Severance charges			8,600
Other operating expenses			5,600
Employment expenses			$ 2,100
RidgeWorth | Forecast
Business Acquisition [Line Items]
Expected increase in goodwill		$ 51,700
RidgeWorth
Business Acquisition [Line Items]
Assets under management	40,100,000
Long term assets under management	35,700,000
Consolidated entity excluding consolidated investment products | RidgeWorth
Business Acquisition [Line Items]
Purchase price	485,200
CLOs
Business Acquisition [Line Items]
Other operating expenses					$ 89
CLOs | RidgeWorth
Business Acquisition [Line Items]
Purchase price	61,900
Trade names | RidgeWorth
Business Acquisition [Line Items]
Indefinite lived intangibles acquired	$ 8,700