Loans and Allowance for Loan Losses (Narrative) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2020 USD ($) contract	Jun. 30, 2019 USD ($) contract	Jun. 30, 2020 USD ($) contract	Jun. 30, 2019 USD ($) contract	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized, cash basis		$ 484,000	$ 996,000	$ 1,400,000	$ 1,600,000
Loans pledged as collateral		15,420,000,000		15,420,000,000				$ 12,110,000,000
Total loans		40,012,482,000		40,012,482,000				37,187,814,000
Allowance for credit loss, reversal		13,300,000
Transfer of third-party lending partnership consumer loans to held for sale loans.		801,000,000.0
Allowance for credit loss, increase		117,800,000		256,500,000
Total allowance for loan losses		588,648,000	257,376,000	588,648,000	257,376,000	$ 493,452,000	$ 281,402,000	281,402,000	$ 257,036,000	$ 250,555,000
Reserve for unfunded commitments		61,000,000.0		61,000,000.0
Allowance for credit losses		649,700,000		649,700,000			$ 282,777,000
Provision for credit losses	[1]	$ 141,851,000	12,119,000	$ 300,573,000	35,688,000
Estimated impact of currently enacted stimulus and an unemployment rate for the end of year		10.00%		10.00%
ACL to loans ratio during period		0.24%
ACL to loans ratio		1.63%		1.63%
ACL to loans ratio, excluding PPP loans		1.74%		1.74%
Recorded Investment		$ 15,652,000	$ 9,225,000	$ 52,348,000	$ 16,732,000
Commitments to land additional funds to TDRs		$ 0		$ 0				0
Troubled Debt Restructuring That Subsequently Defaults
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts | contract		1	1	4	1
Recorded Investment		$ 27,000	$ 5,000	$ 645,000	$ 5,000
Total commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		19,938,276,000		19,938,276,000				$ 16,769,370,000
Recorded Investment		5,390,000	4,014,000	12,588,000	7,645,000
Total commercial and industrial | Small Business Administration (SBA), CARES Act, Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		2,710,000,000		2,710,000,000
Interest Income Recorded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized		$ 2,800,000	$ 3,400,000	$ 4,900,000	$ 5,500,000
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan substandard period (in days)				90 days
Loss and Charged Off
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan charge off (in days)					120 days

[1] Beginning January 1, 2020, provision calculation is based on current expected credit loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.