Note 8 - Reinsurance - Excess-of-Loss Program (Details) $ in Thousands	1 Months Ended					3 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 ($)	Mar. 31, 2021 USD ($) arrangements	Dec. 31, 2020 USD ($)
VIE, Non-consolidated, Carrying Amount, Assets						$ 7,920,861	$ 7,948,021
VIE, Non-consolidated, Carrying Amount, Liabilities						3,685,569	3,663,668
Mortgage segment
Risk In Force						$ 58,500,000	60,700,000
Radian Guaranty | Mortgage segment
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						4
Excess-of-Loss Program | Radian Guaranty | Mortgage segment
VIE, Non-consolidated, Carrying Amount, Assets						$ 1,503,497	1,539,029
VIE, Non-consolidated, Carrying Amount, Liabilities						1,503,497	1,539,029
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Eagle Re 2020-2 (Primary)
Risk In Force		$ 13,011,000				10,458,000	11,748,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		390,000				355,000	390,000
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Eagle Re 2020-2 (Primary) | Variable Interest Entity, Primary Beneficiary
VIE, Non-consolidated, Carrying Amount, Assets						354,792	390,324
VIE, Non-consolidated, Carrying Amount, Liabilities						354,792	390,324
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | 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 | Mortgage segment | Eagle Re 2020-1 (Primary)
Risk In Force			$ 9,866,000			5,156,000	6,121,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured			488,000			488,000	488,000
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | 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 | Mortgage segment | 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 | Mortgage segment | Eagle Re 2019-1 (Primary)
Risk In Force				$ 10,705,000		3,950,000	4,657,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured				562,000		385,000	385,000
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | 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 | Mortgage segment | Eagle Re 2019-1 (Primary) | XOL First Layer
Reinsurance Retention Policy, Amount Retained				$ 268,000		265,000	265,000
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Eagle Re 2018-1 (Primary)
Risk In Force					$ 9,109,000	3,370,000	3,986,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured					434,000	276,000	276,000
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | 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 | Mortgage segment | 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 | Mortgage segment | Eagle Re 2021-1 (Primary) | Subsequent Event
Risk In Force	$ 11,100,000
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	497,700
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Eagle Re 2021-1 (Primary) | Subsequent Event | Third-Party Capital Market
Proceeds from Issuance of Debt	452,300
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Eagle Re 2021-1 (Primary) | Subsequent Event | Radian Group Inc.
Proceeds from Issuance of Debt	$ 45,400
Excess-of-Loss Program | Radian Guaranty | Mortgage segment | Separate Third-Party Reinsurer
Reinsurance Retention Policy, Excess Retention, Amount Reinsured					$ 21,400