Reinsurance - Excess of Loss Reinsurance (Details) - USD ($) $ in Thousands									9 Months Ended	12 Months Ended
	Apr. 01, 2023	Apr. 26, 2022	Apr. 01, 2022	Aug. 03, 2021	Feb. 02, 2021	Oct. 29, 2020	May 25, 2019	Oct. 30, 2018	Sep. 30, 2023	Dec. 31, 2022	Oct. 23, 2023
Home Re 2023-1 | Subsequent Event
Effects of Reinsurance [Line Items]
Excess of loss reinsurance coverage, initial and remaining											$ 330,200
Home Re 2022-1
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes		12 years 6 months
Initial first layer retention		$ 325,589
Remaining first layer retention									$ 325,104	$ 325,576
Excess of loss reinsurance coverage, initial and remaining		$ 473,575							445,461	473,575
Home Re 2021-2
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes				12 years 6 months
Initial first layer retention				$ 190,159
Remaining first layer retention									189,610	190,097
Excess of loss reinsurance coverage, initial and remaining				$ 398,429					281,919	352,084
Home Re 2021-1
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes					12 years 6 months
Initial first layer retention					$ 211,159
Remaining first layer retention									210,858	211,102
Excess of loss reinsurance coverage, initial and remaining					$ 398,848				209,311	277,053
Home Re 2020-1
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes						10 years
Initial first layer retention						$ 275,283
Remaining first layer retention									274,968	275,051
Excess of loss reinsurance coverage, initial and remaining						$ 412,917			53,023	113,247
Home Re 2019-1
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes							10 years
Initial first layer retention							$ 185,730
Remaining first layer retention									182,791	183,540
Excess of loss reinsurance coverage, initial and remaining							$ 315,739		208,146	208,146
Home Re 2018-1
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes								10 years
Initial first layer retention								$ 168,691
Remaining first layer retention									164,385	164,849
Excess of loss reinsurance coverage, initial and remaining								$ 318,636	84,819	140,993
2022 Traditional XOL
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage			10 years
Initial first layer retention			$ 82,523
Remaining first layer retention									82,463	82,517
Excess of loss reinsurance coverage, initial and remaining			$ 142,642						$ 142,642	$ 142,642
2023 Traditional XOL
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage	10 years
Excess of loss reinsurance coverage, initial and remaining	$ 116,000