Noninterest Income - Client Investment Fees (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 285,382	$ 221,371	$ 507,822	$ 438,628
Sweep money market fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19,413	26,952	42,462	53,496
Asset management fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11,596	6,956	20,733	13,628
Repurchase agreement fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	876	11,836	12,083	23,102
Client investment fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 31,885	$ 45,744	$ 75,278	$ 90,226