Loans and Leases (Details 2) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017		Sep. 30, 2017
Financing Receivable, Impaired [Line Items]
Nonaccrual		$ 112,972	$ 155,784	[1]
Loans held for investment		17,230,146	16,972,743
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		155,784
Loans held for investment			16,914,707	[2],[3],[4]	$ 15,628,023
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		17,117,174
Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		16,758,923
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual		32,982
Loans held for investment		7,678,660
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[1],[2]		68,913
Loans held for investment			7,798,991	[2],[4]	6,131,196
Real Estate Mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,645,678
Real Estate Mortgage | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		7,730,078
Real Estate Mortgage | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual		29,723
Loans held for investment		4,932,823
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		65,563
Loans held for investment	[2],[4]		5,361,487
Real Estate Mortgage | Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		4,903,100
Real Estate Mortgage | Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		5,295,924
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Impaired [Line Items]
Nonaccrual		3,259
Loans held for investment		2,745,837
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		3,350
Loans held for investment	[2],[4]		2,437,504
Real Estate Mortgage | Residential Real Estate | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,742,578
Real Estate Mortgage | Residential Real Estate | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		2,434,154
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual		0
Loans held for investment		2,000,957
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[1],[2]		0
Loans held for investment			1,591,229	[2],[4]	1,249,222
Real Estate Construction and Land | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,000,957
Real Estate Construction and Land | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		1,591,229
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual		0
Loans held for investment		854,346
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		0
Loans held for investment	[2],[4]		769,075
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		854,346
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	[2]		769,075
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual		0
Loans held for investment		1,146,611
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		0
Loans held for investment	[2],[4]		822,154
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		1,146,611
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	[2]		822,154
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual		79,718
Loans held for investment		7,152,058
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[1],[2]		86,851
Loans held for investment			7,114,920	[2],[4]	7,861,692
Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,072,340
Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		7,028,069
Commercial | Asset Based
Financing Receivable, Impaired [Line Items]
Nonaccrual		34,619
Loans held for investment		3,222,311
Commercial | Asset Based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		33,553
Loans held for investment	[2],[4]		2,924,871
Commercial | Asset Based | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		3,187,692
Commercial | Asset Based | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		2,891,318
Commercial | Venture Capital Loans
Financing Receivable, Impaired [Line Items]
Nonaccrual		35,520
Loans held for investment		2,031,895
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		29,424
Loans held for investment	[2],[4]		2,122,711
Commercial | Venture Capital Loans | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		1,996,375
Commercial | Venture Capital Loans | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		2,093,287
Commercial | Other Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual		9,579
Loans held for investment		1,897,852
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[2]		23,874
Loans held for investment	[2],[4]		2,067,338
Commercial | Other Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		1,888,273
Commercial | Other Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		2,043,464
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual		272
Loans held for investment		398,471
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual	[1],[2]		20
Loans held for investment			409,567	[2],[4]	$ 385,913
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment		$ 398,199
Consumer | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment	[2]		$ 409,547

[1] Excludes loans held for sale carried at lower of cost or fair value and PCI loans.

[2] Excludes loans held for sale carried at lower of cost or fair value and PCI loans.

[3] Excludes loans held for sale carried at lower of cost or fair value and PCI loans.

[4] Excludes loans held for sale carried at lower of cost or fair value and PCI loans.