Reinsurance - Excess-of-Loss Program (Details) - USD ($) $ in Millions	1 Months Ended						12 Months Ended
	Nov. 30, 2021	Apr. 30, 2021	Oct. 31, 2020	Feb. 29, 2020	Apr. 30, 2019	Nov. 30, 2018	Dec. 31, 2021	Dec. 31, 2020
Mortgage insurance
Ceded Credit Risk [Line Items]
RIF							$ 60,900.0	$ 60,700.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 Ltd. | Radian Group Inc.
Ceded Credit Risk [Line Items]
Proceeds from issuance of debt		$ 45.4
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2021-2 Ltd.
Ceded Credit Risk [Line Items]
RIF	$ 10,758.0						10,379.0	0.0
Initial and remaining coverage	484.0						484.0	0.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2021-1 Ltd.
Ceded Credit Risk [Line Items]
RIF		11,061.0					9,496.0	0.0
Initial and remaining coverage		498.0					498.0	0.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2020-2 Ltd.
Ceded Credit Risk [Line Items]
RIF			$ 13,011.0				7,623.0	11,748.0
Initial and remaining coverage			390.0				144.0	390.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2020-1 Ltd.
Ceded Credit Risk [Line Items]
RIF				$ 9,866.0			3,241.0	6,121.0
Initial and remaining coverage				488.0			488.0	488.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2019-1 Ltd.
Ceded Credit Risk [Line Items]
RIF					$ 10,705.0		2,429.0	4,657.0
Initial and remaining coverage					562.0		385.0	385.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Eagle Re 2018-1 Ltd.
Ceded Credit Risk [Line Items]
RIF						$ 9,109.0	2,117.0	3,986.0
Initial and remaining coverage						434.0	276.0	276.0
Excess-of-Loss Program | Mortgage insurance | Radian Guaranty | Separate Third-Party Reinsurer
Ceded Credit Risk [Line Items]
Initial and remaining coverage						21.4
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2021-2 Ltd.
Ceded Credit Risk [Line Items]
Layer retention	$ 242.0						242.0	0.0
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2021-1 Ltd.
Ceded Credit Risk [Line Items]
Layer retention		$ 221.0					221.0	0.0
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2020-2 Ltd.
Ceded Credit Risk [Line Items]
Layer retention			$ 423.0				423.0	423.0
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2020-1 Ltd.
Ceded Credit Risk [Line Items]
Layer retention				$ 202.0			202.0	202.0
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2019-1 Ltd.
Ceded Credit Risk [Line Items]
Layer retention					$ 268.0		264.0	265.0
Excess-of-Loss Program | XOL First Layer | Mortgage insurance | Radian Guaranty | Eagle Re 2018-1 Ltd.
Ceded Credit Risk [Line Items]
Layer retention						$ 205.0	$ 201.0	$ 201.0