Loans and Allowance for Loan Losses - Summary of Internal Risk-rating Categories (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 9,916,475	$ 9,730,525	$ 9,087,103
Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	7,425,774	7,213,518
Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,770,861	1,580,852
Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	5,106,600	5,073,668
Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	264,309	280,101
Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	264,862	260,207
Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	19,142	18,690
Loss | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,986,366	1,995,016	1,771,122
Commercial and industrial | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,986,366	1,995,016
Commercial and industrial | Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	684,938	655,346
Commercial and industrial | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,171,994	1,199,522
Commercial and industrial | Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	68,826	78,117
Commercial and industrial | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	45,573	47,525
Commercial and industrial | Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	15,035	14,506
Commercial and industrial | Loss | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,676,941	3,573,630	3,523,721
Commercial real estate | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,676,941	3,573,630
Commercial real estate | Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	6,318	6,585
Commercial real estate | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,353,758	3,256,697
Commercial real estate | Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	127,751	134,562
Commercial real estate | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	186,707	173,308
Commercial real estate | Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	2,407	2,478
Commercial real estate | Loss | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	249,416	305,708	293,135
Commercial construction | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	249,416	305,708
Commercial construction | Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Commercial construction | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	232,981	280,792
Commercial construction | Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	10,345	10,330
Commercial construction | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	6,090	14,586
Commercial construction | Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Commercial construction | Loss | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	0	0
Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,513,051	1,339,164	$ 779,916
Business banking | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,513,051	1,339,164
Business banking | Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,079,605	918,921
Business banking | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	347,867	336,657
Business banking | Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	57,387	57,092
Business banking | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	26,492	24,788
Business banking | Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,700	1,706
Business banking | Loss | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 0	$ 0