Loans and Leases (Details 3) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 18,472,852	$ 17,957,713
Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	190,979	237,110
Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	239,304	261,398
Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	18,042,569	17,459,205
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	18,472,852	17,957,713	$ 16,885,192
Real Estate Mortgage
Financing Receivable, Past Due [Line Items]
Loans held for investment	8,076,026	7,918,141
Real Estate Mortgage | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	41,619	68,255
Real Estate Mortgage | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	52,832	75,753
Real Estate Mortgage | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,981,575	7,774,133
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	8,076,026	7,918,141	7,566,374
Real Estate Mortgage | Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	4,435,274	4,824,298
Real Estate Mortgage | Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	32,926	57,734
Real Estate Mortgage | Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	52,477	74,785
Real Estate Mortgage | Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	4,349,871	4,691,779
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		4,824,298
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,640,752	3,093,843
Real Estate Mortgage | Residential Real Estate | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	8,693	10,521
Real Estate Mortgage | Residential Real Estate | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	355	968
Real Estate Mortgage | Residential Real Estate | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,631,704	3,082,354
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		3,093,843
Real Estate Construction and Land
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,376,130	2,233,656
Real Estate Construction and Land | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	390	442
Real Estate Construction and Land | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	5,268	8,568
Real Estate Construction and Land | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,370,472	2,224,646
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,376,130	2,233,656	1,874,026
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment	972,891	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	390	442
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	0	7,041
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	972,501	905,100
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		912,583
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,403,239	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	0	0
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	5,268	1,527
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,397,971	1,319,546
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		1,321,073
Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,574,314	7,404,595
Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	148,395	167,214
Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	180,341	176,062
Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,245,578	7,061,319
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	7,574,314	7,404,595	7,066,112
Commercial | Asset-based
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,606,007	3,305,421
Commercial | Asset-based | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	41,151	45,957
Commercial | Asset-based | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	48,324	48,338
Commercial | Asset-based | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,516,532	3,211,126
Commercial | Asset-based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		3,305,421
Commercial | Venture Capital Loans
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,194,743	2,038,748
Commercial | Venture Capital Loans | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	42,105	28,731
Commercial | Venture Capital Loans | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	68,426	77,588
Commercial | Venture Capital Loans | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,084,212	1,932,429
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		2,038,748
Commercial | Other Commercial
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,773,564	2,060,426
Commercial | Other Commercial | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	65,139	92,526
Commercial | Other Commercial | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	63,591	50,136
Commercial | Other Commercial | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	1,644,834	1,917,764
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment		2,060,426
Consumer
Financing Receivable, Past Due [Line Items]
Loans held for investment		401,321
Consumer | Classified
Financing Receivable, Past Due [Line Items]
Loans held for investment	575	1,199
Consumer | Special Mention
Financing Receivable, Past Due [Line Items]
Loans held for investment	863	1,015
Consumer | Pass
Financing Receivable, Past Due [Line Items]
Loans held for investment	444,944	399,107
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 446,382	$ 401,321	$ 378,680