Business Combinations - Pro Forma Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sustainable Growth Advisers, LP
Business Acquisition [Line Items]
Total Revenues	$ 569,465	$ 454,156
Net Income (Loss) Attributable to Common Stockholders	$ 69,341	26,175
RidgeWorth
Business Acquisition [Line Items]
Total Revenues		489,094	$ 466,429
Net Income (Loss) Attributable to Common Stockholders		$ 27,523	$ 23,511