Loans And Allowance For Loan Losses (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) contract	Dec. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract	Jan. 01, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, impaired, interest lost on nonaccrual loans	$ 12,600,000	$ 6,100,000
Loans pledged as collateral	15,050,000,000.00	12,110,000,000
Modifications, post-modification recorded investment	76,615,000	49,859,000	$ 49,827,000
Provision for losses on loans	336,052,000	87,720,000	51,697,000
Financing Receivable, before Allowance for Credit Loss and Fee	38,330,656,000	37,187,814,000
Transfers to held for sale	1,430,000,000
Provision for credit losses	355,022,000	87,720,000	51,697,000
Purchased credit-impaired loans			0
Allowance for purchased credit-impaired loans		0	0
Provision for Loan, Lease, and Other Losses	355,000,000.0
Investments income recognized in impairment loans, excluding TDRs		0	0
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)	18,300,000
Principal Forgiveness
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modifications, post-modification recorded investment	$ 0	$ 0	$ 0
Troubled Debt Restructuring That Subsequently Defaulted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subsequent default, number of contracts | contract	7,000	4	8
Modifications, post-modification recorded investment	$ 21,700,000	$ 326,000	$ 10,500,000
FCB Financial Holdings, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans				$ 9,290,000,000
Total commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modifications, post-modification recorded investment	28,917,000	28,793,000	21,058,000
Financing Receivable, before Allowance for Credit Loss and Fee	19,373,679,000	16,769,370,000
Total commercial and industrial | Small Business Administration (SBA), CARES Act, Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss and Fee	2,190,000,000
Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modifications, post-modification recorded investment	34,579,000	5,590,000	16,758,000
Financing Receivable, before Allowance for Credit Loss and Fee	10,570,434,000	10,493,784,000
Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modifications, post-modification recorded investment	13,119,000	15,476,000	$ 12,011,000
Financing Receivable, before Allowance for Credit Loss and Fee	$ 8,386,543,000	$ 9,924,660,000