Note 16 - Statutory Information Risk To Capital Calculation (Details) $ in Millions		6 Months Ended
		Jun. 30, 2018 USD ($) state	Dec. 31, 2017 USD ($)
Risk to Capital Line Items [Line Items]
Number Of States That Have A Statutory Or Regulatory Risk Based Capital Requirement | state		16
Risk To Capital Ratio, Regulatory Maximum		25
Radian Guaranty
Risk to Capital Line Items [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Increase (Decrease)		$ 244.1
RIF, net (1)	[1]	38,956.0	$ 36,793.5
Common stock and paid-in capital		1,866.0	1,866.0
Surplus Notes		100.0	100.0
Unassigned earnings (deficit)		(737.4)	(765.0)
Statutory policyholders’ surplus		1,228.6	1,201.0
Contingency reserve		1,883.5	1,667.0
Statutory capital		$ 3,112.1	$ 2,868.0
Risk-to-capital		12.5	12.8
Statutory Accounting Practices, Statutory Net Income Amount		$ 244.5
Non RBC States [Member] | Minimum [Member]
Risk to Capital Line Items [Line Items]
Capital Required for Capital Adequacy		1.0
Non RBC States [Member] | Maximum [Member]
Risk to Capital Line Items [Line Items]
Capital Required for Capital Adequacy		$ 5.0
Reportable Subsegments [Member]
Risk to Capital Line Items [Line Items]
Risk-to-capital		11.8	12.1

[1] Excludes risk ceded through reinsurance contracts (to third parties and affiliates) and RIF on defaulted loans.