Loans and Leases - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($) contract	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($) contract	Jun. 30, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	$ 46,314,000		$ 46,314,000				$ 11,085,000
Receivable, 30-89 days past due	8,576,000		8,576,000				9,788,000
Nonaccrual loans and leases	85,615,000		85,615,000				92,353,000
Allowance for Loan and Lease Losses, Period Increase (Decrease)			44,900,000
Provision	81,000,000	$ 8,000,000	272,000,000	$ 22,000,000
Gross loans and leases held for investment	19,101,680,000		19,101,680,000				18,910,740,000
Loans and Leases Receivable, Allowance	345,966,000	$ 138,552,000	345,966,000	$ 138,552,000	$ 301,050,000	$ 142,402,000	138,785,000	$ 135,037,000	$ 132,472,000
Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans and leases	49,300,000		$ 49,300,000
Percentage of nonaccrual loans and leases			58.00%
Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	46,300,000		$ 46,300,000				11,100,000
Receivable, 30-89 days past due	400,000		400,000				1,200,000
Financing receivable, nonaccrual status, current	38,900,000		$ 38,900,000				80,000,000.0
Real Estate Mortgage Commercial Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract			1
Financing Receivable, Troubled Debt Restructuring, Subsequent Default			$ 412,000
Other Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract		3	1	3
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 133,000	$ 5,000	$ 133,000
Venture Capital Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract				2
Financing Receivable, Troubled Debt Restructuring, Subsequent Default				$ 441,000
Other Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | contract		1
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 254,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	12,999,000		12,999,000				4,164,000
Receivable, 30-89 days past due	2,504,000		2,504,000				2,800,000
Nonaccrual loans and leases	37,759,000		37,759,000				70,672,000
Provision	64,921,000	8,907,000	121,804,000	22,692,000
Gross loans and leases held for investment	7,402,854,000		7,402,854,000				7,714,358,000
Loans and Leases Receivable, Allowance	128,265,000	$ 64,185,000	128,265,000	$ 64,185,000	$ 97,947,000	$ 68,388,000	61,528,000	$ 59,401,000	$ 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 | Other Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable, 90 or more days past due	10,751,000		10,751,000				4,164,000
Receivable, 30-89 days past due	185,000		185,000				2,781,000
Nonaccrual loans and leases	32,941,000		32,941,000				27,594,000
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	2,319,000		2,319,000				0
Nonaccrual loans and leases	$ 2,001,000		$ 2,001,000				$ 12,916,000