Note 16 - Statutory Information - Statutory Financial Statements (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) payment state subsidiaries	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Statutory Accounting Practices [Line Items]
Prepaid federal income taxes (Note 10)		$ 210,889	$ 134,800
Payments Made on Surplus Note | payment		0
Radian Guaranty
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Release of Contingency Reserves		$ 93,000
Related Party Transaction, Rate	3.00%
Number of States in which Entity Operates | state		50
Statutory Accounting Practices, Statutory Net Income Amount		$ 441,900	703,400	$ 501,900
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		481,500	637,700	814,100
Surplus Note	$ 200,000
Radian Reinsurance
Statutory Accounting Practices [Line Items]
Risk In Force	6,000,000
Statutory Accounting Practices, Dividends Paid with Approval of Regulatory Agency	465,000
Statutory Accounting Practices, Statutory Net Income Amount		32,500	101,600	86,100
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		360,700	455,600	356,200
Other MI Companies
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount		1,100	100	(2,800)
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		$ 41,300	45,700	58,000
Radian Title Insurance
Statutory Accounting Practices [Line Items]
Number of States in which Entity Operates | state		39
Statutory Accounting Practices, Statutory Net Income Amount		$ 2,100	300	(1,800)
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		$ 28,800	$ 27,000	$ 27,000
Radian Group Inc.
Statutory Accounting Practices [Line Items]
Marketable Securities	$ 200,000
Minimum | Radian Guaranty
Statutory Accounting Practices [Line Items]
Surplus Note, Notice of Redemption Period	30 days
Differences Between GAAP Basis and SAPP Basis
Statutory Accounting Practices [Line Items]
Mortgage Guaranty Insurance Companies Are Required Each Year To Establish A Contingency Reserve Equal To This Percentage Of Premiums Earned In Such Year		50.00%
Number of Years That a Contingency Reserve Must Be Maintained Under SAPP		10 years
Loss Ratio		35.00%
PENNSYLVANIA
Statutory Accounting Practices [Line Items]
Number of Subsidiaries | subsidiaries		2