Loans and Leases - Credit Risk Rating Categories for Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 18,979,228	$ 19,083,377	$ 19,745,305
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,987,213	7,899,936	8,008,944
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,565,823	3,360,281	2,880,253
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,085,840	7,502,905	8,426,224
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	340,352	320,255	$ 429,884
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	163,117	265,262
Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	86,508	100,310
Classified | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	718	42,558
Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	75,265	121,932
Classified | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	626	462
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	632,997	721,285
Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	317,694	323,846
Special Mention | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	67,392	108,351
Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	245,080	286,356
Special Mention | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,831	2,732
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	18,183,114	18,096,830
Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	7,583,011	7,475,780
Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,497,713	3,209,372
Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	6,765,495	7,094,617
Pass | Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	336,895	317,061
Asset-based | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,383,403	3,429,283
Asset-based | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	24,941	27,867
Asset-based | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	142,122	153,301
Asset-based | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,216,340	3,248,115
Venture Capital Loans | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,495,798	1,698,508
Venture Capital Loans | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	8,727	6,508
Venture Capital Loans | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	89,423	118,125
Venture Capital Loans | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	1,397,648	1,573,875
Other Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,206,639	2,375,114
Other Commercial | Classified | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	41,597	87,557
Other Commercial | Special Mention | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	13,535	14,930
Other Commercial | Pass | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,151,507	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	990,035	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	302	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	66,790	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	922,943	966,971
Residential Real Estate Construction Financing Receivable | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,575,788	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	416	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	602	759
Residential Real Estate Construction Financing Receivable | Pass | Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	2,574,770	2,242,401
Commercial | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,941,610	4,096,671
Commercial | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	77,444	91,543
Commercial | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	254,463	262,462
Commercial | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	3,609,703	3,742,666
Residential Real Estate | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	4,045,603	3,803,265
Residential Real Estate | Classified | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	9,064	8,767
Residential Real Estate | Special Mention | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	63,231	61,384
Residential Real Estate | Pass | Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment, net	$ 3,973,308	3,733,114
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment, net		$ 19,083,377