Loans and Leases (Details 3) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 18,735,543	$ 17,957,713
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	188,607	237,110
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	267,925	261,398
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	18,279,011	17,459,205
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	18,735,543	17,957,713	$ 17,230,146
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,896,924	7,918,141
Real Estate Mortgage | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	43,622	68,255
Real Estate Mortgage | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	40,314	75,753
Real Estate Mortgage | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,812,988	7,774,133
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,896,924	7,918,141	7,678,660
Real Estate Mortgage | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	4,300,566	4,824,298
Real Estate Mortgage | Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	34,952	57,734
Real Estate Mortgage | Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	39,309	74,785
Real Estate Mortgage | Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	4,226,305	4,691,779
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		4,824,298
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,596,358	3,093,843
Real Estate Mortgage | Residential Real Estate | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	8,670	10,521
Real Estate Mortgage | Residential Real Estate | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,005	968
Real Estate Mortgage | Residential Real Estate | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,586,683	3,082,354
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		3,093,843
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,551,474	2,233,656
Real Estate Construction and Land | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	377	442
Real Estate Construction and Land | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	837	8,568
Real Estate Construction and Land | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,550,260	2,224,646
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,551,474	2,233,656	2,000,957
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,009,362	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	377	442
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	0	7,041
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,008,985	905,100
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		912,583
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,542,112	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	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	837	1,527
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,541,275	1,319,546
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		1,321,073
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,878,557	7,404,595
Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	143,830	167,214
Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	226,160	176,062
Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,508,567	7,061,319
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,878,557	7,404,595	7,152,058
Commercial | Asset-based
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,810,741	3,305,421
Commercial | Asset-based | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	50,634	45,957
Commercial | Asset-based | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	41,974	48,338
Commercial | Asset-based | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,718,133	3,211,126
Commercial | Asset-based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		3,305,421
Commercial | Venture Capital Loans
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,209,649	2,038,748
Commercial | Venture Capital Loans | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	34,489	28,731
Commercial | Venture Capital Loans | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	66,255	77,588
Commercial | Venture Capital Loans | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,108,905	1,932,429
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		2,038,748
Commercial | Other Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,858,167	2,060,426
Commercial | Other Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	58,707	92,526
Commercial | Other Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	117,931	50,136
Commercial | Other Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,681,529	1,917,764
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		2,060,426
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment		401,321
Consumer | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	778	1,199
Consumer | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	614	1,015
Consumer | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	407,196	399,107
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 408,588	$ 401,321	$ 398,471