Loans and Leases - Credit Risk Rating Categories for Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 19,506,257	$ 19,083,377	$ 19,694,631
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,413,020	7,899,936	7,955,734
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,505,584	3,360,281	3,340,528
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,222,244	7,502,905	7,987,050
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	365,409	320,255	$ 411,319
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	147,267	265,262
Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	75,508	100,310
Classified | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,218	42,558
Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	69,064	121,932
Classified | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	477	462
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	536,052	721,285
Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	303,002	323,846
Special Mention | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	75,526	108,351
Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	154,984	286,356
Special Mention | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,540	2,732
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,822,938	18,096,830
Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,034,510	7,475,780
Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,427,840	3,209,372
Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,998,196	7,094,617
Pass | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	362,392	317,061
Asset-based | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,550,903	3,429,283
Asset-based | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	24,351	27,867
Asset-based | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	102,734	153,301
Asset-based | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,423,818	3,248,115
Venture Capital Loans | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,749,432	1,698,508
Venture Capital Loans | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	5,708	6,508
Venture Capital Loans | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	33,910	118,125
Venture Capital Loans | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,709,814	1,573,875
Other Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,921,909	2,375,114
Other Commercial | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	39,005	87,557
Other Commercial | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,340	14,930
Other Commercial | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,864,564	2,272,627
Commercial Real Estate Construction Loan Receivable | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	930,785	1,117,121
Commercial Real Estate Construction Loan Receivable | Classified | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	284	42,558
Commercial Real Estate Construction Loan Receivable | Special Mention | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	67,292	107,592
Commercial Real Estate Construction Loan Receivable | Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	863,209	966,971
Residential Real Estate Construction Financing Receivable | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,574,799	2,243,160
Residential Real Estate Construction Financing Receivable | Classified | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,934	0
Residential Real Estate Construction Financing Receivable | Special Mention | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,234	759
Residential Real Estate Construction Financing Receivable | Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,564,631	2,242,401
Commercial | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,792,198	4,096,671
Commercial | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	62,827	91,543
Commercial | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	242,159	262,462
Commercial | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,487,212	3,742,666
Residential Real Estate [Member] | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,620,822	3,803,265
Residential Real Estate [Member] | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	12,681	8,767
Residential Real Estate [Member] | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	60,843	61,384
Residential Real Estate [Member] | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 4,547,298	3,733,114
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment, net		$ 19,083,377