Loans and Leases - Aging Analysis of Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Delinquent loans in loan portfolio
30-89 Days Past Due	$ 8,576	$ 9,788
90 or More Days Past Due	46,314	11,085
Total Past Due	54,890	20,873
Current	18,971,310	18,825,999
Loans held for investment, net	19,026,200	18,846,872	$ 18,735,543
Real Estate Mortgage
Delinquent loans in loan portfolio
30-89 Days Past Due	2,173	4,553
90 or More Days Past Due	33,199	6,721
Total Past Due	35,372	11,274
Current	7,841,673	7,961,473
Loans held for investment, net	7,877,045	7,972,747	7,896,924
Real Estate Mortgage | Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	412	2,448
90 or More Days Past Due	32,662	5,919
Total Past Due	33,074	8,367
Current	4,159,392	4,194,320
Loans held for investment, net	4,192,466	4,202,687
Real Estate Mortgage | Residential Real Estate
Delinquent loans in loan portfolio
30-89 Days Past Due	1,761	2,105
90 or More Days Past Due	537	802
Total Past Due	2,298	2,907
Current	3,682,281	3,767,153
Loans held for investment, net	3,684,579	3,770,060
Real Estate Construction and Land
Delinquent loans in loan portfolio
30-89 Days Past Due	3,108	1,429
90 or More Days Past Due	0	0
Total Past Due	3,108	1,429
Current	3,420,639	2,736,373
Loans held for investment, net	3,423,747	2,737,802	2,551,474
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Delinquent loans in loan portfolio
30-89 Days Past Due	0	0
90 or More Days Past Due	0	0
Total Past Due	0	0
Current	1,241,647	1,082,368
Loans held for investment, net	1,241,647	1,082,368
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Delinquent loans in loan portfolio
30-89 Days Past Due	3,108	1,429
90 or More Days Past Due	0	0
Total Past Due	3,108	1,429
Current	2,178,992	1,654,005
Loans held for investment, net	2,182,100	1,655,434
Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	2,504	2,800
90 or More Days Past Due	12,999	4,164
Total Past Due	15,503	6,964
Current	7,347,671	7,688,532
Loans held for investment, net	7,363,174	7,695,496	7,878,557
Commercial | Asset-based
Delinquent loans in loan portfolio
30-89 Days Past Due	0	19
90 or More Days Past Due	2,248	0
Total Past Due	2,248	19
Current	3,150,800	3,748,388
Loans held for investment, net	3,153,048	3,748,407
Commercial | Venture Capital Loans
Delinquent loans in loan portfolio
30-89 Days Past Due	2,319	0
90 or More Days Past Due	0	0
Total Past Due	2,319	0
Current	1,634,813	2,179,422
Loans held for investment, net	1,637,132	2,179,422
Commercial | Other Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	185	2,781
90 or More Days Past Due	10,751	4,164
Total Past Due	10,936	6,945
Current	2,562,058	1,760,722
Loans held for investment, net	2,572,994	1,767,667
Consumer
Delinquent loans in loan portfolio
30-89 Days Past Due	791	1,006
90 or More Days Past Due	116	200
Total Past Due	907	1,206
Current	361,327	439,621
Loans held for investment, net	$ 362,234	$ 440,827	$ 408,588