Noninterest Income - Client Investment Fees (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 247,037	$ 205,905	$ 756,847	$ 644,533
Sweep money market fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18,155	26,202	60,617	79,698
Asset management fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12,172	7,256	32,905	20,883
Repurchase agreement fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,587	13,221	13,670	36,324
Client investment fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 31,914	$ 46,679	$ 107,192	$ 136,905