Amounts Related to Cumulative Basis Adjustments for Fair Value Hedges (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Carrying amount of hedged liabilities	$ 91.3	$ 90.5
Cumulative basis adjustment included in the carrying amount	$ (1.3)	$ (0.5)

Amount of liability hedged in fair value hedging relationship.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109999712-113959

Name:	us-gaap_HedgedLiabilityFairValueHedge
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant