Reserve for Known and Incurred but Not Reported Claims - Summary of Incurred and Paid Claims Development Net of Reinsurance (Detail) Claim in Millions, $ in Millions	Dec. 31, 2023 USD ($) Claim	Dec. 31, 2022 USD ($)	[1]	Dec. 31, 2021 USD ($)	[1]	Dec. 31, 2020 USD ($)	[1]	Dec. 31, 2019 USD ($)	[1]	Dec. 31, 2018 USD ($)	[1]	Dec. 31, 2017 USD ($)	[1]	Dec. 31, 2016 USD ($)	[1]	Dec. 31, 2015 USD ($)	[1]	Dec. 31, 2014 USD ($)	[1]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 1,781.9
Cumulative paid claims and allocated claim adjustment expenses	1,766.2
All outstanding liabilities before 2014	0.0
Liabilities for claims and claims adjustment expenses	40.4
Home warranty
Claims Development [Line Items]
Liabilities for claims and claims adjustment expenses	15.7
Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 123.8	$ 123.8		$ 123.8		$ 123.8		$ 123.8		$ 123.8		$ 123.8		$ 123.8		$ 123.8		$ 123.8
Cumulative number of reported claims | Claim	0.8
Cumulative paid claims and allocated claim adjustment expenses	$ 123.8	123.8		123.8		123.8		123.8		123.8		123.8		123.8		123.8		$ 111.2
Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 143.7	143.7		143.7		143.7		143.7		143.7		143.7		143.7		143.7
Cumulative number of reported claims | Claim	0.9
Cumulative paid claims and allocated claim adjustment expenses	$ 143.7	143.7		143.7		143.7		143.7		143.7		143.7		143.7		$ 129.5
Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 172.7	172.7		172.7		172.7		172.7		172.7		172.7		172.7
Cumulative number of reported claims | Claim	1.0
Cumulative paid claims and allocated claim adjustment expenses	$ 172.7	172.7		172.7		172.7		172.7		172.7		172.7		$ 155.4
Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 167.2	167.2		167.2		167.2		167.2		167.2		167.2
Cumulative number of reported claims | Claim	1.0
Cumulative paid claims and allocated claim adjustment expenses	$ 167.2	167.2		167.2		167.2		167.2		167.2		$ 151.1
Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 179.8	179.8		179.8		179.8		179.8		179.8
Cumulative number of reported claims | Claim	1.1
Cumulative paid claims and allocated claim adjustment expenses	$ 179.8	179.8		179.8		179.8		179.8		$ 163.0
Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 174.1	174.1		174.1		174.1		174.1
Cumulative number of reported claims | Claim	1.1
Cumulative paid claims and allocated claim adjustment expenses	$ 174.1	174.1		174.1		174.1		$ 159.2
Accident Year 2020 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 197.4	197.4		197.4		197.4
Cumulative number of reported claims | Claim	1.2
Cumulative paid claims and allocated claim adjustment expenses	$ 197.4	197.4		197.4		$ 177.8
Accident Year 2021 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 218.2	218.2		218.2
Cumulative number of reported claims | Claim	1.2
Cumulative paid claims and allocated claim adjustment expenses	$ 218.2	218.2		$ 198.7
Accident Year 2022 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 211.8	211.8
Cumulative number of reported claims | Claim	1.1
Cumulative paid claims and allocated claim adjustment expenses	$ 211.8	$ 192.3
Accident Year 2023 [Member]
Claims Development [Line Items]
Incurred claims and allocated claim adjustment expenses	$ 193.2
Cumulative number of reported claims | Claim	1.0
Cumulative paid claims and allocated claim adjustment expenses	$ 177.5

[1] Amounts unaudited.