Loans and Allowance for Loan Losses - Summary of Internal Risk-rating Categories (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 9,504,562	$ 9,730,525
Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	6,946,317	7,213,518
Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,046,000	1,580,852
Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	5,441,602	5,073,668
Special mention | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	202,780	280,101
Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	238,329	260,207
Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	17,606	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	1,652,447	1,995,016
Commercial and Industrial | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,652,447	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	278,093	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	1,302,413	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	13,959	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	41,459	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	16,523	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	3,825,186	3,573,630
Commercial Real Estate | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,825,186	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	4,196	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	3,524,607	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	124,618	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	171,765	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	0	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	243,146	305,708
Commercial Construction | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	243,146	305,708
Commercial Construction | Unrated | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	138	0
Commercial Construction | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	224,770	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	9,611	10,330
Commercial Construction | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	8,627	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	1,225,538	1,339,164
Business Banking | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,225,538	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	763,573	918,921
Business Banking | Pass | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	389,812	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	54,592	57,092
Business Banking | Substandard | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	16,478	24,788
Business Banking | Doubtful | Nonperforming Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,083	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