Note 16 - Statutory Information - Risk To Capital Calculation (Details) - Radian Guaranty $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Risk to Capital Line Items [Line Items]
RIF, net	$ 48,914.0		$ 44,076.7
Common stock and paid-in capital	1,041.0		1,041.0
Surplus Note	300.0	$ 200.0	100.0
Unassigned earnings (deficit)	(857.6)		(503.3)
Statutory policyholders’ surplus	483.4		637.7
Contingency reserve	3,212.1		2,607.8
Statutory capital	$ 3,695.5		$ 3,245.5
Risk-to-capital	13.2		13.6
Increase (decrease) in Statutory Capital and Surplus	$ 450.0
Statutory Net Income (Loss)	260.2
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	$ 0.0