Note 18 - Statutory Information Statutory Financial Statements (Details) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) state subsidiaries	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Radian Insurance
Statutory Accounting Practices [Line Items]
Risk In Force		$ 10.2
Radian Guaranty
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount		703.4	$ 501.9	$ 445.1
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		637.7	814.1	1,201.0
Contingency Reserve		2,607.8	2,109.9	1,667.0
Surplus Note		100.0	100.0
Radian Reinsurance
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount		101.6	86.1	64.3
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		455.6	356.2	328.9
Contingency Reserve		360.3	293.5	234.0
Other MI Companies
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount		0.1	(2.8)	0.1
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		45.7	58.0	58.6
Contingency Reserve		1.8	$ 1.7	$ 1.7
Radian Title Insurance
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount		0.3
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		$ 27.0
Number of States in which Entity Operates | state		39
Subsequent Event | Radian Guaranty
Statutory Accounting Practices [Line Items]
Surplus Note	$ 200.0
Related Party Transaction, Rate	3.00%
Subsequent Event | Radian Reinsurance
Statutory Accounting Practices [Line Items]
Risk In Force	$ 6,000.0
Statutory Accounting Practices, Dividends Paid with Approval of Regulatory Agency	465.0
Subsequent Event | Radian Group Inc.
Statutory Accounting Practices [Line Items]
Marketable Securities	$ 200.0
Minimum | Subsequent Event | 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