Loans and Leases - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($) contract	Jun. 30, 2020 USD ($) contract	Jun. 30, 2019 USD ($) contract	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	$ 27,456,000		$ 27,456,000			$ 11,085,000
Receivable, 30-89 days past due	60,550,000		60,550,000			9,788,000
Nonaccrual loans and leases	166,113,000		166,113,000			92,353,000
Allowance for Loan and Lease Losses, Period Increase (Decrease)			79,800,000
Provision	93,000,000	$ 10,000,000	191,000,000	$ 14,000,000
Gross loans and leases held for investment	19,780,476,000		19,780,476,000			18,910,740,000
Loans and Leases Receivable, Allowance	301,050,000	$ 135,037,000	301,050,000	$ 135,037,000	$ 221,292,000	138,785,000	$ 136,281,000	$ 132,472,000
Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans and leases	86,500,000		$ 86,500,000
Percentage of nonaccrual loans and leases			52.00%
Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	27,500,000		$ 27,500,000			11,100,000
Receivable, 30-89 days past due	52,600,000		52,600,000			1,200,000
Financing receivable, nonaccrual status, current	86,000,000.0		$ 86,000,000.0			80,000,000.0
Venture Capital Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract		2	1	2
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 447,000	$ 2,000,000.0	$ 447,000
Other Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract		1		3
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 81,000		$ 140,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	19,602,000		19,602,000			4,164,000
Receivable, 30-89 days past due	15,627,000		15,627,000			2,800,000
Nonaccrual loans and leases	101,278,000		101,278,000			70,672,000
Provision	19,424,000	8,752,000	56,883,000	13,785,000
Gross loans and leases held for investment	8,033,592,000		8,033,592,000			7,714,358,000
Loans and Leases Receivable, Allowance	97,947,000	$ 59,401,000	97,947,000	$ 59,401,000	$ 87,570,000	61,528,000	$ 61,496,000	$ 56,360,000
Commercial | Finance Receivable, Payroll Protection Program Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans and leases held for investment	1,200,000,000		1,200,000,000
Commercial | Venture Capital Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	0		0			0
Receivable, 30-89 days past due	3,939,000		3,939,000			0
Nonaccrual loans and leases	8,270,000		8,270,000			12,916,000
Commercial | Other Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	1,877,000		1,877,000			4,164,000
Receivable, 30-89 days past due	7,991,000		7,991,000			2,781,000
Nonaccrual loans and leases	$ 73,995,000		$ 73,995,000			$ 27,594,000