Intangible Assets - Summary Of Gross Goodwill And Accumulated Impairment Losses And Write-Offs Detailed By Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 1,432,787	$ 1,386,853	$ 191,371
Additions	0	45,934	1,195,482
Goodwill, Ending balance	1,432,787	1,432,787	1,386,853
Regional Banking
Goodwill [Roll Forward]
Goodwill, Beginning balance	1,289,819	1,243,885	93,367
Additions	0	45,934	1,150,518
Goodwill, Ending balance	1,289,819	1,289,819	1,243,885
Fixed Income
Goodwill [Roll Forward]
Goodwill, Beginning balance	142,968	142,968	98,004
Additions	0	0	44,964
Goodwill, Ending balance	$ 142,968	$ 142,968	$ 142,968