Loans and Leases (Details 2) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Impaired [Line Items]
Nonaccrual	$ 81,265	$ 79,333
Loans held for investment	18,472,852	17,957,713
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		79,333
Loans held for investment	18,472,852	17,957,713	$ 16,885,192
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	18,391,587
Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		17,878,380
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	19,895
Loans held for investment	8,076,026	7,918,141
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		17,845
Loans held for investment	8,076,026	7,918,141	7,566,374
Real Estate Mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	8,056,131
Real Estate Mortgage | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,900,296
Real Estate Mortgage | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	17,012
Loans held for investment	4,435,274	4,824,298
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		15,321
Loans held for investment		4,824,298
Real Estate Mortgage | Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	4,418,262
Real Estate Mortgage | Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		4,808,977
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,883
Loans held for investment	3,640,752	3,093,843
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		2,524
Loans held for investment		3,093,843
Real Estate Mortgage | Residential Real Estate | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	3,637,869
Real Estate Mortgage | Residential Real Estate | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		3,091,319
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	390
Loans held for investment	2,376,130	2,233,656
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		442
Loans held for investment	2,376,130	2,233,656	1,874,026
Real Estate Construction and Land | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	2,375,740
Real Estate Construction and Land | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,233,214
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	390
Loans held for investment	972,891	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		442
Loans held for investment		912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	972,501
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		912,141
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	0
Loans held for investment	1,403,239	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		0
Loans held for investment		1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	1,403,239
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		1,321,073
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	60,536
Loans held for investment	7,574,314	7,404,595
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		60,003
Loans held for investment	7,574,314	7,404,595	7,066,112
Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	7,513,778
Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,344,592
Commercial | Asset-based
Financing Receivable, Impaired [Line Items]
Nonaccrual	32,236
Loans held for investment	3,606,007	3,305,421
Commercial | Asset-based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		32,324
Loans held for investment		3,305,421
Commercial | Asset-based | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	3,573,771
Commercial | Asset-based | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		3,273,097
Commercial | Venture Capital Loans
Financing Receivable, Impaired [Line Items]
Nonaccrual	22,501
Loans held for investment	2,194,743	2,038,748
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		20,299
Loans held for investment		2,038,748
Commercial | Venture Capital Loans | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	2,172,242
Commercial | Venture Capital Loans | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,018,449
Commercial | Other Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	5,799
Loans held for investment	1,773,564	2,060,426
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		7,380
Loans held for investment		2,060,426
Commercial | Other Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	1,767,765
Commercial | Other Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,053,046
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	444
Loans held for investment		401,321
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		1,043
Loans held for investment	446,382	401,321	$ 378,680
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	$ 445,938
Consumer | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		$ 400,278