Note 8 - Reinsurance - Excess-of-Loss Program (Details) $ in Thousands	1 Months Ended					9 Months Ended	12 Months Ended
	Apr. 30, 2021 USD ($)	Oct. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Apr. 30, 2019 USD ($)	Nov. 30, 2018 USD ($)	Sep. 30, 2021 USD ($) arrangements	Dec. 31, 2020 USD ($)
VIE, Non-consolidated, Carrying Amount, Assets						$ 8,041,608	$ 7,948,021
VIE, Non-consolidated, Carrying Amount, Liabilities						$ 3,783,672	3,663,668
Radian Guaranty
Reinsurance Retention Policy, Term of Coverage, Period						10 years
Excess-of-Loss Program | Radian Guaranty
Number of Fully Collateralized Reinsurance Arrangements with the Eagle Re Issuers | arrangements						5
VIE, Non-consolidated, Carrying Amount, Assets						$ 1,852,021	1,539,029
VIE, Non-consolidated, Carrying Amount, Liabilities						1,852,021	1,539,029
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 (Primary)
Risk In Force	$ 11,061,000					9,999,000	0
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	498,000					498,000	0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 (Primary) | Radian Group Inc.
Proceeds from Issuance of Debt	45,400
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						497,735	0
VIE, Non-consolidated, Carrying Amount, Liabilities						497,735	0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained	$ 221,000					221,000	0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-2 (Primary)
Risk In Force		$ 13,011,000				8,451,000	11,748,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		390,000				206,000	390,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-2 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						205,581	390,324
VIE, Non-consolidated, Carrying Amount, Liabilities						205,581	390,324
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-2 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained		$ 423,000				423,000	423,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-1 (Primary)
Risk In Force			$ 9,866,000			3,727,000	6,121,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured			488,000			488,000	488,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-1 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						488,385	488,385
VIE, Non-consolidated, Carrying Amount, Liabilities						488,385	488,385
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-1 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained			$ 202,000			202,000	202,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2019-1 (Primary)
Risk In Force				$ 10,705,000		2,787,000	4,657,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured				562,000		385,000	385,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2019-1 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						384,602	384,602
VIE, Non-consolidated, Carrying Amount, Liabilities						384,602	384,602
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2019-1 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained				$ 268,000		264,000	265,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2018-1 (Primary)
Risk In Force					$ 9,109,000	2,415,000	3,986,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured					434,000	276,000	276,000
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2018-1 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						275,718	275,718
VIE, Non-consolidated, Carrying Amount, Liabilities						275,718	275,718
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2018-1 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained					205,000	$ 201,000	$ 201,000
Excess-of-Loss Program | Radian Guaranty | Separate Third-Party Reinsurer
Reinsurance Retention Policy, Excess Retention, Amount Reinsured					$ 21,400