Loans and Leases (Details 1) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Delinquent loans in loan portfolio
30-89 Days Past Due	$ 17,625	$ 6,600
90 or More Days Past Due	10,917	10,700
Total Past Due	28,542
Current	18,707,001
Loans held for investment, net	18,735,543	17,957,713
Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		17,085
90 or More Days Past Due		10,723
Total Past Due		27,808
Current		17,929,905
Loans held for investment, net	18,735,543	17,957,713	$ 17,230,146
Real Estate Mortgage
Delinquent loans in loan portfolio
30-89 Days Past Due	7,418
90 or More Days Past Due	7,606
Total Past Due	15,024
Current	7,881,900
Loans held for investment, net	7,896,924	7,918,141
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		5,044
90 or More Days Past Due		8,017
Total Past Due		13,061
Current		7,905,080
Loans held for investment, net	7,896,924	7,918,141	7,678,660
Real Estate Mortgage | Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	2,867
90 or More Days Past Due	7,137
Total Past Due	10,004
Current	4,290,562
Loans held for investment, net	4,300,566	4,824,298
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		3,487
90 or More Days Past Due		7,541
Total Past Due		11,028
Current		4,813,270
Loans held for investment, net		4,824,298
Real Estate Mortgage | Residential Real Estate
Delinquent loans in loan portfolio
30-89 Days Past Due	4,551
90 or More Days Past Due	469
Total Past Due	5,020
Current	3,591,338
Loans held for investment, net	3,596,358	3,093,843
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		1,557
90 or More Days Past Due		476
Total Past Due		2,033
Current		3,091,810
Loans held for investment, net		3,093,843
Real Estate Construction and Land
Delinquent loans in loan portfolio
30-89 Days Past Due	2,622
90 or More Days Past Due	0
Total Past Due	2,622
Current	2,548,852
Loans held for investment, net	2,551,474	2,233,656
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		1,527
90 or More Days Past Due		442
Total Past Due		1,969
Current		2,231,687
Loans held for investment, net	2,551,474	2,233,656	2,000,957
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Delinquent loans in loan portfolio
30-89 Days Past Due	0
90 or More Days Past Due	0
Total Past Due	0
Current	1,009,362
Loans held for investment, net	1,009,362	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		0
90 or More Days Past Due		442
Total Past Due		442
Current		912,141
Loans held for investment, net		912,583
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Delinquent loans in loan portfolio
30-89 Days Past Due	2,622
90 or More Days Past Due	0
Total Past Due	2,622
Current	1,539,490
Loans held for investment, net	1,542,112	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		1,527
90 or More Days Past Due		0
Total Past Due		1,527
Current		1,319,546
Loans held for investment, net		1,321,073
Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	6,790
90 or More Days Past Due	2,903
Total Past Due	9,693
Current	7,868,864
Loans held for investment, net	7,878,557	7,404,595
Commercial | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		9,933
90 or More Days Past Due		1,931
Total Past Due		11,864
Current		7,392,731
Loans held for investment, net	7,878,557	7,404,595	7,152,058
Commercial | Asset-based
Delinquent loans in loan portfolio
30-89 Days Past Due	48
90 or More Days Past Due	662
Total Past Due	710
Current	3,810,031
Loans held for investment, net	3,810,741	3,305,421
Commercial | Asset-based | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		47
90 or More Days Past Due		646
Total Past Due		693
Current		3,304,728
Loans held for investment, net		3,305,421
Commercial | Venture Capital Loans
Delinquent loans in loan portfolio
30-89 Days Past Due	0
90 or More Days Past Due	0
Total Past Due	0
Current	2,209,649
Loans held for investment, net	2,209,649	2,038,748
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		4,705
90 or More Days Past Due		0
Total Past Due		4,705
Current		2,034,043
Loans held for investment, net		2,038,748
Commercial | Other Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	6,742
90 or More Days Past Due	2,241
Total Past Due	8,983
Current	1,849,184
Loans held for investment, net	1,858,167	2,060,426
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		5,181
90 or More Days Past Due		1,285
Total Past Due		6,466
Current		2,053,960
Loans held for investment, net		2,060,426
Consumer
Delinquent loans in loan portfolio
30-89 Days Past Due	795
90 or More Days Past Due	408
Total Past Due	1,203
Current	407,385
Loans held for investment, net		401,321
Consumer | Non Purchased Credit Impaired Loans and Leases
Delinquent loans in loan portfolio
30-89 Days Past Due		581
90 or More Days Past Due		333
Total Past Due		914
Current		400,407
Loans held for investment, net	$ 408,588	$ 401,321	$ 398,471