Business Combinations - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	7 Months Ended	12 Months Ended
	Jun. 01, 2017	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Acquisition related adjustments				$ 0	$ (87)	$ 0
Goodwill		$ 170,153	$ 170,153	170,153	6,788	6,701	$ 5,260
RidgeWorth
Business Acquisition [Line Items]
Purchase price, consideration transferred	$ 547,100	$ 51,700
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
Consideration transferred, deferred cash	2,300
Acquisition related adjustments			1,000
Goodwill	163,365
Acquisition costs included in goodwill for tax purposes	6,400
Transaction and integration costs				26,300
Severance costs				10,200
Other operating expenses				9,700
Employment expenses				6,400
Revenue since closing date			$ 77,100
RidgeWorth
Business Acquisition [Line Items]
Assets under management	40,100,000
Long term assets under management	35,700,000
Liquidity strategy assets under management	4,400,000
Consolidated entity excluding consolidated investment products
Business Acquisition [Line Items]
Other operating expenses				69,410	$ 50,274	$ 63,901
Consolidated entity excluding consolidated investment products | RidgeWorth
Business Acquisition [Line Items]
Purchase price, consideration transferred	485,200
CLOs
Business Acquisition [Line Items]
Other operating expenses				$ 6,684
CLOs | RidgeWorth
Business Acquisition [Line Items]
Purchase price, consideration transferred	$ 61,900