Note 8 - Reinsurance - Single Premium QSR Program (Details) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended			15 Months Ended	33 Months Ended	36 Months Ended
	Dec. 31, 2017	Jan. 31, 2020	Oct. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2017
Ceded Credit Risk [Line Items]
Ceded Premiums Written				$ 87,201	$ 56,132	$ 98,314
Radian Guaranty | 2020 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
Ceded Premiums Written		$ 250,000
Concentration Risk, Percentage		65.00%
Ceding commission for premium ceded		25.00%
RIF Ceded				1,597,000	0
Radian Guaranty | 2020 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio		56.00%
Radian Guaranty | 2018 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage			65.00%
Ceding commission for premium ceded			25.00%
RIF Ceded				$ 1,979,000	3,231,000
Radian Guaranty | 2018 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio			56.00%
Radian Guaranty | 2016 Single Premium QSR Transaction
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	65.00%						20.00%	35.00%	35.00%
Ceding commission for premium ceded				25.00%
RIF Ceded				$ 3,071,000	$ 5,351,000
Radian Guaranty | 2016 Single Premium QSR Transaction | Maximum
Ceded Credit Risk [Line Items]
Loss Ratio				55.00%