Losses and LAE - Net Outstanding Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total gross reserve for losses and LAE	$ 828,642	$ 848,413
Mortgage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reinsurance recoverables on unpaid claims	66,676	71,769	$ 14,594	$ 11,009
Unallocated LAE	20,104
Total gross reserve for losses and LAE	823,136	$ 844,107	$ 401,273	$ 397,891
Mortgage insurance | Mortgage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserve for losses and LAE, net of reinsurance	$ 736,356