Loans and Allowance for Credit Losses - Summary of Average Recorded Investment in Impaired Originated and ANCI Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	$ 58,196	$ 122,297	$ 171,634
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	55,906	119,540	169,483
Commercial and Industrial | General C&I
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	10,834	8,586	11,291
Commercial and Industrial | Energy Sector
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	27,348	108,751	158,192
Commercial and Industrial | Restaurant Industry
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	16,600	2,203
Commercial and Industrial | Healthcare
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	1,124
Consumer
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	1,870	1,812	1,604
Consumer | Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	1,557	1,426	1,206
Consumer | Other
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	313	386	398
Small Business Lending
Accounts Notes And Loans Receivable [Line Items]
Average recorded investment	$ 420	$ 945	$ 547