Regulatory Information - Schedule of Combined Statutory Net Loss, Statutory Surplus, Contingency Reserve and RTC Ratios (Details) - NMIC and Re One Combined
$ in Thousands
12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Statutory Accounting Practices [Line Items]      
Statutory net gain (loss) $ 15,233 $ (19,784) $ (35,946)
Statutory surplus 449,602 430,785 371,084
Contingency reserve $ 531,825 $ 332,702 $ 186,641
Risk-to-capital 15.8 13.1 13.2