Loans and Leases - Aging Analysis of Loans and Leases Held for Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Delinquent loans in loan portfolio
30-89 Days Past Due	$ 60,550	$ 9,788
90 or More Days Past Due	27,456	11,085
Total Past Due	88,006	20,873
Current	19,606,625	18,825,999
Loans held for investment, net	19,694,631	18,846,872	$ 18,472,852
Real Estate Mortgage
Delinquent loans in loan portfolio
30-89 Days Past Due	42,834	4,553
90 or More Days Past Due	7,639	6,721
Total Past Due	50,473	11,274
Current	7,905,261	7,961,473
Loans held for investment, net	7,955,734	7,972,747	8,076,026
Real Estate Mortgage | Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	42,784	2,448
90 or More Days Past Due	6,985	5,919
Total Past Due	49,769	8,367
Current	4,172,306	4,194,320
Loans held for investment, net	4,222,075	4,202,687
Real Estate Mortgage | Residential Real Estate
Delinquent loans in loan portfolio
30-89 Days Past Due	50	2,105
90 or More Days Past Due	654	802
Total Past Due	704	2,907
Current	3,732,955	3,767,153
Loans held for investment, net	3,733,659	3,770,060
Real Estate Construction and Land
Delinquent loans in loan portfolio
30-89 Days Past Due	1,022	1,429
90 or More Days Past Due	0	0
Total Past Due	1,022	1,429
Current	3,339,506	2,736,373
Loans held for investment, net	3,340,528	2,737,802	2,376,130
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	1,167,609	1,082,368
Loans held for investment, net	1,167,609	1,082,368
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Delinquent loans in loan portfolio
30-89 Days Past Due	1,022	1,429
90 or More Days Past Due	0	0
Total Past Due	1,022	1,429
Current	2,171,897	1,654,005
Loans held for investment, net	2,172,919	1,655,434
Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	15,627	2,800
90 or More Days Past Due	19,602	4,164
Total Past Due	35,229	6,964
Current	7,951,821	7,688,532
Loans held for investment, net	7,987,050	7,695,496	7,574,314
Commercial | Asset-based
Delinquent loans in loan portfolio
30-89 Days Past Due	3,697	19
90 or More Days Past Due	17,725	0
Total Past Due	21,422	19
Current	3,391,009	3,748,388
Loans held for investment, net	3,412,431	3,748,407
Commercial | Venture Capital Loans
Delinquent loans in loan portfolio
30-89 Days Past Due	3,939	0
90 or More Days Past Due	0	0
Total Past Due	3,939	0
Current	1,810,402	2,179,422
Loans held for investment, net	1,814,341	2,179,422
Commercial | Other Commercial
Delinquent loans in loan portfolio
30-89 Days Past Due	7,991	2,781
90 or More Days Past Due	1,877	4,164
Total Past Due	9,868	6,945
Current	2,750,410	1,760,722
Loans held for investment, net	2,760,278	1,767,667
Consumer
Delinquent loans in loan portfolio
30-89 Days Past Due	1,067	1,006
90 or More Days Past Due	215	200
Total Past Due	1,282	1,206
Current	410,037	439,621
Loans held for investment, net	$ 411,319	$ 440,827	$ 446,382