Revenue from Contracts with Customers - Narrative (Detail) - Other Assets - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Insurance commission earned but not yet received	$ 12.9	$ 15.8
Cash Management Fees
Disaggregation of Revenue [Line Items]
Fess earned but not yet received	0.9	1.0
Debit Card
Disaggregation of Revenue [Line Items]
Fess earned but not yet received	$ 0.3	$ 0.3

For an unclassified balance sheet, the amount of fees and other revenue, excluding investment income receivable, earned but not yet received, which were recognized in conformity with revenue recognition criteria based on estimates or specific contractual terms.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_AccruedFeesAndOtherRevenueReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant