Intangible Assets - Summary Of Gross Goodwill And Accumulated Impairment Losses And Write-Offs Detailed By Reportable Segments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 1,432,787	$ 1,386,853
Additions	0	22,969
Goodwill, Ending balance	1,432,787	1,409,822
Regional Banking
Goodwill [Roll Forward]
Goodwill, Beginning balance	1,289,819	1,243,885
Additions	0	22,969
Goodwill, Ending balance	1,289,819	1,266,854
Fixed Income
Goodwill [Roll Forward]
Goodwill, Beginning balance	142,968	142,968
Additions	0	0
Goodwill, Ending balance	$ 142,968	$ 142,968