Loans and Leases - Nonaccrual and Performing Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable, Impaired [Line Items]
Nonaccrual	$ 64,507	$ 91,163	$ 85,615
Loans held for investment, net	20,511,020	19,083,377	19,026,200
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	33,162	45,557	47,128
Loans held for investment, net	9,580,957	7,899,936	7,877,045
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	19,918	315	324
Loans held for investment, net	3,651,873	3,360,281	3,423,747
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	10,932	44,902	37,759
Loans held for investment, net	6,872,222	7,502,905	7,363,174
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	495	389	404
Loans held for investment, net	405,968	320,255	$ 362,234
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	20,446,513	18,992,214
Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	9,547,795	7,854,379
Performing | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,631,955	3,359,966
Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	6,861,290	7,458,003
Performing | Consumer
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	405,473	319,866
Asset-based | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	1,605	2,679
Loans held for investment, net	3,661,769	3,429,283
Asset-based | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,660,164	3,426,604
Venture Capital Loans | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,348	1,980
Loans held for investment, net	1,632,861	1,698,508
Venture Capital Loans | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,630,513	1,696,528
Other Commercial | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	6,979	40,243
Loans held for investment, net	1,577,592	2,375,114
Other Commercial | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,570,613	2,334,871
Commercial Real Estate Construction Loan Receivable | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	315
Loans held for investment, net	992,003	1,117,121
Commercial Real Estate Construction Loan Receivable | Performing | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	992,003	1,116,806
Residential Real Estate Construction Financing Receivable | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	19,918	0
Loans held for investment, net	2,659,870	2,243,160
Residential Real Estate Construction Financing Receivable | Performing | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	2,639,952	2,243,160
Commercial | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	25,615	43,731
Loans held for investment, net	3,694,597	4,096,671
Commercial | Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,668,982	4,052,940
Residential Real Estate [Member] | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	7,547	1,826
Loans held for investment, net	5,886,360	3,803,265
Residential Real Estate [Member] | Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	$ 5,878,813	$ 3,801,439