Loans and Leases - Credit Risk Rating Categories for Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 19,694,631	$ 18,846,872	$ 18,472,852
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	293,230	175,912
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	766,397	322,956
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,635,004	18,348,004
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,955,734	7,972,747	8,076,026
Real Estate Mortgage | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	78,387	42,135
Real Estate Mortgage | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	328,462	31,781
Real Estate Mortgage | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,548,885	7,898,831
Real Estate Mortgage | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,222,075	4,202,687
Real Estate Mortgage | Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	71,446	33,535
Real Estate Mortgage | Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	322,312	30,070
Real Estate Mortgage | Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,828,317	4,139,082
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,733,659	3,770,060
Real Estate Mortgage | Residential Real Estate | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,941	8,600
Real Estate Mortgage | Residential Real Estate | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,150	1,711
Real Estate Mortgage | Residential Real Estate | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,720,568	3,759,749
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,340,528	2,737,802	2,376,130
Real Estate Construction and Land | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	337	364
Real Estate Construction and Land | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	12,354	1,429
Real Estate Construction and Land | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,327,837	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	1,167,609	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	337	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	12,354	0
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,154,918	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	2,172,919	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	2,172,919	1,654,005
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,987,050	7,695,496	7,574,314
Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	213,876	132,800
Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	407,529	288,534
Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,365,645	7,274,162
Commercial | Asset-based
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,412,431	3,748,407
Commercial | Asset-based | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	25,008	32,223
Commercial | Asset-based | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	186,813	38,936
Commercial | Asset-based | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,200,610	3,677,248
Commercial | Venture Capital Loans
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,814,341	2,179,422
Commercial | Venture Capital Loans | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	29,054	35,316
Commercial | Venture Capital Loans | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	138,403	74,813
Commercial | Venture Capital Loans | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,646,884	2,069,293
Commercial | Other Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,760,278	1,767,667
Commercial | Other Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	159,814	65,261
Commercial | Other Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	82,313	174,785
Commercial | Other Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,518,151	1,527,621
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	411,319	440,827	$ 446,382
Consumer | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	630	613
Consumer | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,052	1,212
Consumer | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 392,637	439,002
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment, net		$ 18,846,872