Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 16,542,593	$ 14,625,032
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	4,143,983	3,590,375
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	10,902,893	9,912,309
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,495,717	1,122,348
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	16,251,917	14,349,491
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	3,982,453	3,399,426
Pass | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	10,781,587	9,828,744
Pass | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,487,877	1,121,321
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	119,088	63,103
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	33,718	31,996
Special Mention | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	77,884	30,892
Special Mention | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	7,486	215
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	109,425	144,842
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	66,511	92,320
Substandard | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	42,560	51,710
Substandard | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	354	812
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	62,163	67,596
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	61,301	66,633
Doubtful | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	862	963
Doubtful | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 0	$ 0