Regulatory Information - Narrative (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2019
USD ($)
state
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Statutory Accounting Practices [Line Items]        
Maximum permitted RTC ratio 25      
Number of states which require minimum amount of statutory capital relative to risk in force | state 16      
Mortgage insurance, percentage of indebtedness on single loan 25.00%      
Shareholders' equity $ 930,420 $ 701,500 $ 509,077 $ 475,509
Dividends, restriction with regards to capital surplus 10.00%      
Dividends, restriction with regards to capital surplus $ 16,100      
NMIC        
Statutory Accounting Practices [Line Items]        
Mortgage insurance risk in force $ 15,400,000 $ 10,000,000    
Risk-to-capital 16.3 13.7