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Allowance for Credit Losses (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Detail) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2022 | Mar. 31, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | $ 299,653 | $ 379,910
Other adjustments | 22 | 30
Charge-offs | (4,725) | (16,116)
Recoveries | 2,193 | 2,771
Provision for credit losses | 4,025 | (45,386)
Allowance for credit losses at period end | 301,168 | 321,209
Individually measured | 5,152 | 8,329
Collectively measured | 296,016 | 312,880
Loans at period end, individually measured | 72,846 | 124,404
Loans at period end, collectively measured | 35,149,717 | 32,994,913
Loans held at fair value | 57,984 | 51,916
Commercial |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 119,307 | 94,212
Other adjustments | 0 | 0
Charge-offs | (1,414) | (11,781)
Recoveries | 538 | 452
Provision for credit losses | 2,480 | 12,757
Allowance for credit losses at period end | 120,911 | 95,640
Individually measured | 3,698 | 5,046
Collectively measured | 117,213 | 90,594
Loans at period end, individually measured | 19,651 | 30,144
Loans at period end, collectively measured | 11,564,312 | 12,678,063
Loans held at fair value | 0 | 0
Commercial real estate |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 144,583 | 243,603
Other adjustments | 0 | 0
Charge-offs | (777) | (980)
Recoveries | 32 | 200
Provision for credit losses | 1,068 | (61,031)
Allowance for credit losses at period end | 144,906 | 181,792
Individually measured | 522 | 2,042
Collectively measured | 144,384 | 179,750
Loans at period end, individually measured | 22,370 | 43,858
Loans at period end, collectively measured | 9,212,704 | 8,500,921
Loans held at fair value | 0 | 0
Home equity |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 10,699 | 11,437
Other adjustments | 0 | 0
Charge-offs | (197) | 0
Recoveries | 93 | 101
Provision for credit losses | (29) | (156)
Allowance for credit losses at period end | 10,566 | 11,382
Individually measured | 127 | 338
Collectively measured | 10,439 | 11,044
Loans at period end, individually measured | 12,904 | 21,167
Loans at period end, collectively measured | 308,531 | 369,086
Loans held at fair value | 0 | 0
Residential real estate |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 8,782 | 12,459
Other adjustments | 0 | 0
Charge-offs | (466) | (2)
Recoveries | 5 | 204
Provision for credit losses | 1,108 | 1,581
Allowance for credit losses at period end | 9,429 | 14,242
Individually measured | 800 | 822
Collectively measured | 8,629 | 13,420
Loans at period end, individually measured | 17,842 | 28,675
Loans at period end, collectively measured | 1,724,159 | 1,341,382
Loans held at fair value | 57,984 | 51,916
Premium finance receivables |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 15,859 | 17,777
Other adjustments | 22 | 30
Charge-offs | (1,678) | (3,239)
Recoveries | 1,476 | 1,782
Provision for credit losses | (957) | 1,127
Allowance for credit losses at period end | 14,722 | 17,477
Individually measured | 0 | 0
Collectively measured | 14,722 | 17,477
Loans at period end, individually measured | 0 | 0
Loans at period end, collectively measured | 12,291,571 | 10,070,038
Loans held at fair value | 0 | 0
Consumer and other |  |
Financing Receivable, Allowance for Credit Loss [Roll Forward] |  |
Allowance for credit losses at beginning of period | 423 | 422
Other adjustments | 0 | 0
Charge-offs | (193) | (114)
Recoveries | 49 | 32
Provision for credit losses | 355 | 336
Allowance for credit losses at period end | 634 | 676
Individually measured | 5 | 81
Collectively measured | 629 | 595
Loans at period end, individually measured | 79 | 560
Loans at period end, collectively measured | 48,440 | 35,423
Loans held at fair value | $ 0 | $ 0

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- Definition Amount excluding accrued interest, of allowance for credit loss on financing receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
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- Definition The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
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- Definition Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
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- Definition Amount of increase in allowance for credit loss on financing receivable from recovery. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
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- Definition Amount of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
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