Loans and Leases (Details 3) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 19,745,305	$ 18,846,872	$ 18,307,697
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	147,705	175,912
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	898,658	322,956
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,698,942	18,348,004
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,008,944	7,972,747	8,159,458
Real Estate Mortgage | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	40,991	42,135
Real Estate Mortgage | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	374,159	31,781
Real Estate Mortgage | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,593,794	7,898,831
Real Estate Mortgage | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,220,649	4,202,687
Real Estate Mortgage | Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	33,908	33,535
Real Estate Mortgage | Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	371,668	30,070
Real Estate Mortgage | Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,815,073	4,139,082
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,788,295	3,770,060
Real Estate Mortgage | Residential Real Estate | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,083	8,600
Real Estate Mortgage | Residential Real Estate | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,491	1,711
Real Estate Mortgage | Residential Real Estate | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,778,721	3,759,749
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,880,253	2,737,802	2,351,724
Real Estate Construction and Land | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	351	364
Real Estate Construction and Land | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	10,577	1,429
Real Estate Construction and Land | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,869,325	2,736,009
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,087,505	1,082,368
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	351	364
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	10,577	0
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,076,577	1,082,004
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,792,748	1,655,434
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	0	0
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	0	1,429
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,792,748	1,654,005
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,426,224	7,695,496	7,424,354
Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	105,826	132,800
Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	512,451	288,534
Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,807,947	7,274,162
Commercial | Asset-based
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,938,402	3,748,407
Commercial | Asset-based | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	23,218	32,223
Commercial | Asset-based | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	152,136	38,936
Commercial | Asset-based | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,763,048	3,677,248
Commercial | Venture Capital Loans
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,715,837	2,179,422
Commercial | Venture Capital Loans | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	31,110	35,316
Commercial | Venture Capital Loans | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	173,947	74,813
Commercial | Venture Capital Loans | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,510,780	2,069,293
Commercial | Other Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,771,985	1,767,667
Commercial | Other Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	51,498	65,261
Commercial | Other Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	186,368	174,785
Commercial | Other Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,534,119	1,527,621
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	429,884	440,827	$ 372,161
Consumer | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	537	613
Consumer | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,471	1,212
Consumer | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 427,876	439,002
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment, net		$ 18,846,872