Loans and Leases (Details 2) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Impaired [Line Items]
Nonaccrual	$ 95,602	$ 92,353
Loans held for investment, net	19,745,305	18,846,872	$ 18,307,697
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	19,649,703	18,754,519
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	21,396	20,824
Loans held for investment, net	8,008,944	7,972,747	8,159,458
Real Estate Mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	7,987,548	7,951,923
Real Estate Mortgage | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	19,088	18,346
Loans held for investment, net	4,220,649	4,202,687
Real Estate Mortgage | Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	4,201,561	4,184,341
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,308	2,478
Loans held for investment, net	3,788,295	3,770,060
Real Estate Mortgage | Residential Real Estate | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,785,987	3,767,582
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	351	364
Loans held for investment, net	2,880,253	2,737,802	2,351,724
Real Estate Construction and Land | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	2,879,902	2,737,438
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	351	364
Loans held for investment, net	1,087,505	1,082,368
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,087,154	1,082,004
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Loans held for investment, net	1,792,748	1,655,434
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,792,748	1,655,434
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	73,442	70,672
Loans held for investment, net	8,426,224	7,695,496	7,424,354
Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	8,352,782	7,624,824
Commercial | Asset-based
Financing Receivable, Impaired [Line Items]
Nonaccrual	17,104	30,162
Loans held for investment, net	3,938,402	3,748,407
Commercial | Asset-based | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	3,921,298	3,718,245
Commercial | Venture Capital Loans
Financing Receivable, Impaired [Line Items]
Nonaccrual	18,612	12,916
Loans held for investment, net	2,715,837	2,179,422
Commercial | Venture Capital Loans | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	2,697,225	2,166,506
Commercial | Other Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	37,726	27,594
Loans held for investment, net	1,771,985	1,767,667
Commercial | Other Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	1,734,259	1,740,073
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	413	493
Loans held for investment, net	429,884	440,827	$ 372,161
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	$ 429,471	$ 440,334