Loans and Leases (Details 3) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018		Mar. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 18,307,697	$ 17,957,713
Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	190,305	237,110
Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	292,780	261,398
Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	17,824,612	17,459,205
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		17,957,713	[1]	$ 16,455,285
Real Estate Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	8,159,458	7,918,141
Real Estate Mortgage | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	33,673	68,255
Real Estate Mortgage | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	67,567	75,753
Real Estate Mortgage | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	8,058,218	7,774,133
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		7,918,141		7,554,243
Real Estate Mortgage | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	4,640,510	4,824,298
Real Estate Mortgage | Commercial | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	24,542	57,734
Real Estate Mortgage | Commercial | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	67,115	74,785
Real Estate Mortgage | Commercial | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	4,548,853	4,691,779
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		4,824,298
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	3,518,948	3,093,843
Real Estate Mortgage | Residential Real Estate | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	9,131	10,521
Real Estate Mortgage | Residential Real Estate | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	452	968
Real Estate Mortgage | Residential Real Estate | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	3,509,365	3,082,354
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		3,093,843
Real Estate Construction and Land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	2,351,724	2,233,656
Real Estate Construction and Land | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	430	442
Real Estate Construction and Land | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	2,485	8,568
Real Estate Construction and Land | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	2,348,809	2,224,646
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		2,233,656		1,677,002
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	943,596	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	430	442
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Special Mention
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Loans held for investment	943,166	905,100
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		912,583
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	1,408,128	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Classified
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Loans held for investment	2,485	1,527
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	1,405,643	1,319,546
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		1,321,073
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	7,424,354	7,404,595
Commercial | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	155,404	167,214
Commercial | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	222,091	176,062
Commercial | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	7,046,859	7,061,319
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		7,404,595		6,826,123
Commercial | Asset Based
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	3,422,202	3,305,421
Commercial | Asset Based | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	52,586	45,957
Commercial | Asset Based | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	85,060	48,338
Commercial | Asset Based | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	3,284,556	3,211,126
Commercial | Asset Based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		3,305,421
Commercial | Venture Capital Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	2,027,450	2,038,748
Commercial | Venture Capital Loans | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	43,128	28,731
Commercial | Venture Capital Loans | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	62,514	77,588
Commercial | Venture Capital Loans | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	1,921,808	1,932,429
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		2,038,748
Commercial | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	1,974,702	2,060,426
Commercial | Other Commercial | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	59,690	92,526
Commercial | Other Commercial | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	74,517	50,136
Commercial | Other Commercial | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	1,840,495	1,917,764
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		2,060,426
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	372,161	401,321
Consumer | Classified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	798	1,199
Consumer | Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	637	1,015
Consumer | Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment	$ 370,726	399,107
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment		$ 401,321		$ 397,917

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