Loans (Narrative) (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Loans [Line Items]
Net deferred loan fees and costs and fair value accounting adjustments	$ 70.9	$ 71.8	$ 59.3
Premium finance receivables
Loans [Line Items]
Unearned income portion of premium finance receivables	$ 244.0	$ 224.5	$ 140.3

Amount of unamortized loan commitment, origination, and other costs (fees) and purchase premium (discount) on financing receivable recognized as adjustment to yield. Excludes financing receivable covered under loss sharing agreement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=84159169&loc=d3e10152-111534

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant