Losses and LAE - Narrative (Details)	12 Months Ended
Dec. 31, 2021 payment default state	Dec. 31, 2020 default	Dec. 31, 2019 default
Number of states \| state	0
Number of payments missed for insured loans	2
Minimum
Number of payments missed for insured loans	2
Mortgage \| CALIFORNIA \| New Insurance Written \| Geographic Concentration Risk
Concentration risk, percentage	10.90%	10.40%	10.60%
Mortgage \| CALIFORNIA \| Minimum \| Primary Risk In Force \| Geographic Concentration Risk
Concentration risk, percentage	10.00%	10.00%
Primary Mortgage Product \| Mortgage
New primary default notices \| default	37,470	108,025	40,985
New defaults	8.00%	8.50%	7.50%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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