Loans and Allowance for Credit Losses - Schedule of Past Due Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	$ 157,240	$ 206,569
Past Due 90 Days or More and Accruing	570	1,353
Nonaccrual	126,412	157,484
Current	11,960,284	12,037,323
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	34,523	54,596
Past Due 90 Days or More and Accruing	20	258
Nonaccrual	21,023	24,954
Current	2,299,766	2,193,808
Consumer Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	5,466	5,937
Past Due 90 Days or More and Accruing	107	456
Nonaccrual	3,785	3,087
Current	553,555	583,385
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	12,304	11,966
Past Due 90 Days or More and Accruing	154	377
Nonaccrual	3,527	2,595
Current	1,004,983	1,047,667
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	2,701	2,690
Past Due 90 Days or More and Accruing	108	170
Nonaccrual	1,074	1,599
Current	147,138	152,022
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	41,023	42,606
Past Due 90 Days or More and Accruing		52
Nonaccrual	39,036	38,648
Current	2,849,273	3,190,364
Commercial Real Estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	13,116	13,824
Nonaccrual	12,929	13,824
Current	699,976	490,801
Commercial Real Estate [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	48,107	74,950
Past Due 90 Days or More and Accruing	181	40
Nonaccrual	45,038	72,777
Current	4,405,593	4,379,276
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	25,049	40,443
30 to 59 Days Past Due [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	11,054	25,947
30 to 59 Days Past Due [Member] | Consumer Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,020	1,434
30 to 59 Days Past Due [Member] | Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	7,704	7,091
30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,372	711
30 to 59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	1,489	3,627
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	187
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	2,223	1,633
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	5,209	7,289
60 to 89 Days Past Due [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	2,426	3,437
60 to 89 Days Past Due [Member] | Consumer Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	554	960
60 to 89 Days Past Due [Member] | Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	919	1,903
60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	147	210
60 to 89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	498	279
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivables, Past Due	$ 665	$ 500