Loans and Allowance for Credit Losses - Total Acquired Credit Impaired Loans Outstanding by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	$ 13,710,243	$ 10,089,117	$ 8,677,400
ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	303,783	203,275
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	7,481,688	6,197,342	5,500,775
Commercial and Industrial | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	42,969	16,807
Commercial and Industrial | General C&I
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	4,423,086	3,275,362
Commercial and Industrial | General C&I | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	41,440	16,807
Commercial and Industrial | Restaurant Industry
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	1,137,898	1,096,366
Commercial and Industrial | Restaurant Industry | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	1,529
Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,830,195	1,330,739	1,156,410
Commercial Real Estate | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	109,020	65,427
Commercial Real Estate | Income Producing
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,481,360	1,266,791
Commercial Real Estate | Income Producing | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	96,780	65,427
Commercial Real Estate | Land and Development
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	348,835	63,948
Commercial Real Estate | Land and Development | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	12,240
Consumer
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,639,518	2,294,753	1,784,878
Consumer | Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,518,347	2,227,653
Consumer | Other
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	121,171	67,100
Consumer | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	131,457	121,041
Consumer | ACI | Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	130,484	120,495
Consumer | ACI | Other
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	973	546
Small Business Lending
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	758,842	$ 266,283	$ 235,337
Small Business Lending | ACI
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	$ 20,337