Loans and Allowance for Credit Losses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 segment	Dec. 31, 2020	Dec. 31, 2020 portfolio	Dec. 31, 2020 application
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan portfolios | portfolio						4
Number of loan segments				7		7
Total loans, net of unearned income	$ 13,786,479,000	$ 12,117,524,000
Accrued interest receivable, loans	$ 57,300,000
Loan placed on nonaccrual when past due, number of days	90 days
Loan participations	$ 1,043,000,000.000
Loan participations sold	478,900,000
Loan participations retained	563,600,000
Financing receivable TDR's included with non-accrual loans	14,900,000	13,800,000
Financing receivable troubled debt restructurings specific reserves	1,600,000	900,000
Unfunded commitments on TDRs	0	2,300,000
Recoveries from credit losses	(38,395,000)		$ (6,966,000)
Charge-offs	(5,450,000)		(431,000)
Allowance for loan losses charge-offs	$ 15,553,000		12,969,000
Number of days for a loan to be considered to be in payment default	90 days
Troubled Debt Restructurings During Period
Financing Receivable, Allowance for Credit Losses [Line Items]
Recoveries from credit losses	$ 300,000	2,000,000.0
Charge-offs	0	3,900,000	0
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
PPP, number of applications processed and approved (over) | application							9,700
PPP, amount of funding	1,500,000,000
Total loans, net of unearned income	3,956,422,000	2,890,296,000
Recoveries from credit losses	(4,022,000)		(4,064,000)
Charge-offs	(633,000)		169,000
Allowance for loan losses charge-offs	5,593,000		3,087,000
Commercial | PPP Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	943,000,000.0
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	5,946,512,000	$ 5,166,792,000
Percentage of risk-based capital					222.00%
Regulatory guideline limit					300.00%
Recoveries from credit losses	(29,535,000)		(173,000)
Charge-offs	(4,801,000)		(561,000)
Allowance for loan losses charge-offs	$ 4,323,000		$ 879,000
Credit Concentration Risk | Non Residential Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Concentration risk percentage	10.00%
Credit Concentration Risk | Residential Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Concentration risk percentage	10.00%