Note 8 - Reinsurance QSR Reinsurance Transaction Details (Details) $ in Thousands			1 Months Ended		12 Months Ended			15 Months Ended	24 Months Ended	33 Months Ended	36 Months Ended
		Dec. 31, 2017 USD ($)	Jan. 31, 2020 USD ($) group	Oct. 31, 2017	Dec. 31, 2019 USD ($) group	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2013	Dec. 31, 2017 USD ($)	Dec. 31, 2015	Dec. 31, 2017 USD ($)
Ceded Credit Risk [Line Items]
Ceded Premiums Written	[1]				$ 56,132	$ 98,314	$ 214,343
Radian Guaranty | QSR Program
Ceded Credit Risk [Line Items]
RIF Ceded		$ 1,200,000			600,000	900,000	1,200,000		$ 1,200,000		$ 1,200,000
Radian Guaranty | 2016 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
RIF Ceded		$ 6,900,000			$ 5,400,000	6,300,000	$ 6,900,000		$ 6,900,000		$ 6,900,000
Concentration Risk, Percentage		65.00%						20.00%	35.00%	35.00%	35.00%
Ceding commission for premium ceded					25.00%
Radian Guaranty | 2016 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio					55.00%
Radian Guaranty | 2018 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
RIF Ceded					$ 3,200,000	$ 1,900,000
Ceding commission for premium ceded				25.00%
Number of GSEs | group					1
Percentage of NIW Able to be Ceded Under QSA				65.00%
Radian Guaranty | 2018 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio				56.00%
Subsequent Event | Radian Guaranty | 2020 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
Ceding commission for premium ceded			25.00%
Number of GSEs | group			1
Percentage of NIW Able to be Ceded Under QSA			65.00%
Ceded Premiums Written			$ 250,000
Subsequent Event | Radian Guaranty | 2020 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio			56.00%

[1] Net of profit commission.