Loans Receivable and Allowance for Credit Losses (Narrative) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($) loan borrower	Mar. 31, 2021 USD ($) loan	Dec. 31, 2021 USD ($) loan borrower	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of nonaccrual loans	$ 44,300,000		$ 48,000,000
Loans less than 90 days past due	$ 20,300,000		$ 23,000,000
Number of loans 90 days past due and still accruing | loan	0		0
Impaired loan defined floor limit (greater than)	$ 1,000,000
Impaired loans number | loan	134		155
Impaired loans	$ 48,323,000		$ 52,254,000
Number of troubled debt restructurings | loan	105		132
Number of borrowers | borrower	102
Troubled debt restructurings			$ 30,600,000
Collateral-dependent impaired loans	$ 16,200,000		18,200,000
Provision benefit to operations	(6,400,000)	$ (15,000,000)
Charge off, impaired loan	$ 0	$ 1,500,000
Number of payment defaults for loans modified as TDRs | loan	0	0
Allowances for loan losses	$ 2,034,000		4,284,000
Impaired financing receivable with no related allowance	34,100,000		34,200,000
Average balance of impaired loans	$ 51,575,000		53,352,000
Number of PPP loans | loan	2,067
Paycheck protection program	$ 682,000,000
Number of loans forgiven | loan	1,994
Paycheck protection program, amount forgiven	$ 653,100,000
Paycheck protection program, amount outstanding	28,900,000
Total gross loans	9,662,882,000		9,581,624,000
Allowance for credit losses	76,275,000	$ 85,591,000	$ 80,740,000	$ 101,466,000
Performing Financial Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of troubled debt restructurings | loan			115
Number of borrowers | borrower			111
Troubled debt restructurings	20,300,000		$ 21,900,000
Purchased credit-impaired (PCI) loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total gross loans	242,700,000		246,900,000
Allowance for credit losses	2,800,000		2,800,000
Consumer Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent impaired loans	64,000
Commercial Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent impaired loans	14,400,000
Residential Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent impaired loans	1,700,000
Impaired Loans Troubled Debt Restructurings
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	0
Commercial Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	9,147,000		16,420,000
Provision benefit to operations	(4,404,000)	(467,000)
Allowances for loan losses	1,145,000		3,358,000
Average balance of impaired loans	12,226,000		16,018,000
Allowance for credit losses	$ 23,799,000	$ 26,302,000	$ 26,343,000	$ 27,084,000