Loans and Leases - Nonaccrual and Performing Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Financing Receivable, Impaired [Line Items]
Nonaccrual	$ 56,803	$ 91,163	$ 166,113
Loans held for investment, net	19,506,257	19,083,377	19,694,631
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	38,198	45,557	63,978
Loans held for investment, net	8,413,020	7,899,936	7,955,734
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,218	315	337
Loans held for investment, net	3,505,584	3,360,281	3,340,528
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	16,027	44,902	101,278
Loans held for investment, net	7,222,244	7,502,905	7,987,050
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	360	389	520
Loans held for investment, net	365,409	320,255	$ 411,319
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	19,449,454	18,992,214
Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	8,374,822	7,854,379
Performing | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,503,366	3,359,966
Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	7,206,217	7,458,003
Performing | Consumer
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	365,049	319,866
Asset-based | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	1,973	2,679
Loans held for investment, net	3,550,903	3,429,283
Asset-based | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,548,930	3,426,604
Venture Capital Loans | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,717	1,980
Loans held for investment, net	1,749,432	1,698,508
Venture Capital Loans | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,746,715	1,696,528
Other Commercial | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	11,337	40,243
Loans held for investment, net	1,921,909	2,375,114
Other Commercial | Performing | Commercial
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,910,572	2,334,871
Commercial Real Estate Construction Loan Receivable | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	284	315
Loans held for investment, net	930,785	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	930,501	1,116,806
Residential Real Estate Construction Financing Receivable | Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	1,934	0
Loans held for investment, net	2,574,799	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	2,572,865	2,243,160
Commercial | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	32,065	43,731
Loans held for investment, net	3,792,198	4,096,671
Commercial | Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,760,133	4,052,940
Residential Real Estate [Member] | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	6,133	1,826
Loans held for investment, net	4,620,822	3,803,265
Residential Real Estate [Member] | Performing | Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	$ 4,614,689	$ 3,801,439