Loans and Allowance for Credit Losses - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) portfolio application segment	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) loan portfolio application segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) application
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan portfolios | portfolio	4		4
Number of loan segments | segment	7		7
Total loans	$ 13,584,828,000		$ 13,584,828,000		$ 13,786,479,000
Accrued interest receivable on loans	47,200,000		$ 47,200,000		57,300,000
Loan placed on nonaccrual when past due, number of days			90 days
Loan participations	1,124,000,000		$ 1,124,000,000
Loan participations sold	529,700,000		529,700,000
Loan participations retained	594,300,000		$ 594,300,000
TDR term			6 months
Minimum number of days for loan charge off to be recorded			120 days
Maximum number of days for loan charge off to be recorded			180 days
Financing receivable TDRs included with non-accrual loans	12,800,000		$ 12,800,000		14,900,000
Financing receivable TDR specific reserves	800,000		800,000		1,600,000
Unfunded commitments on TDRs	0		$ 0		$ 0
Financing receivable, TDR, number of loans qualified for removal | loan			1
Charge-offs	$ (56,000)	$ (3,259,000)	$ (79,000)	$ (1,351,000)
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]
Charge-offs			$ 0
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
PPP, number of applications processed and approved (over) | application	6,200		6,200		9,700
PPP, amount of funding	$ 583,700,000		$ 583,700,000		$ 1,500,000,000
Total loans	3,505,183,000		3,505,183,000		3,956,422,000
Charge-offs	(1,000)	(1,326,000)	(1,000)	(632,000)
Commercial | PPP Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	354,900,000		354,900,000		943,000,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 6,290,632,000		$ 6,290,632,000		$ 5,946,512,000
Percentage of risk-based capital	233.00%		233.00%
Regulatory guideline limit	300.00%		300.00%
Charge-offs	$ (58,000)	$ (1,993,000)	$ (72,000)	$ (741,000)