Loans and Leases - Credit Risk Rating Categories for Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 20,511,020	$ 19,083,377	$ 19,026,200
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	9,580,957	7,899,936	7,877,045
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,651,873	3,360,281	3,423,747
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,872,222	7,502,905	7,363,174
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	405,968	320,255	$ 362,234
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	141,604	265,262
Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	82,662	100,310
Classified | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	19,918	42,558
Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	38,500	121,932
Classified | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	524	462
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	496,366	721,285
Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	275,860	323,846
Special Mention | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	74,973	108,351
Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	143,368	286,356
Special Mention | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,165	2,732
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	19,873,050	18,096,830
Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	9,222,435	7,475,780
Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,556,982	3,209,372
Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,690,354	7,094,617
Pass | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	403,279	317,061
Asset-based | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,661,769	3,429,283
Asset-based | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,734	27,867
Asset-based | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	87,980	153,301
Asset-based | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,569,055	3,248,115
Venture Capital Loans | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,632,861	1,698,508
Venture Capital Loans | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,840	6,508
Venture Capital Loans | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	38,281	118,125
Venture Capital Loans | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,589,740	1,573,875
Other Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,577,592	2,375,114
Other Commercial | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	28,926	87,557
Other Commercial | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	17,107	14,930
Other Commercial | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,531,559	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	992,003	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	0	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	67,649	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	924,354	966,971
Residential Real Estate Construction Financing Receivable | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,659,870	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	19,918	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	7,324	759
Residential Real Estate Construction Financing Receivable | Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,632,628	2,242,401
Commercial | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,694,597	4,096,671
Commercial | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	69,059	91,543
Commercial | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	202,029	262,462
Commercial | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,423,509	3,742,666
Residential Real Estate [Member] | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	5,886,360	3,803,265
Residential Real Estate [Member] | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	13,603	8,767
Residential Real Estate [Member] | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	73,831	61,384
Residential Real Estate [Member] | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 5,798,926	3,733,114
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment, net		$ 19,083,377