Loss Reserves - Aging of Primary Default Inventory (Details) - loan	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Aging of the Primary Default Inventory [Abstract]
3 months or less	7,586	11,542	9,447
4 - 11 months	7,990	34,620	9,664
12 months or more	17,714	11,548	10,917
Total primary default inventory	33,290	57,710	30,028	32,898
3 months or less (in hundredths)	23.00%	20.00%	32.00%
4 - 11 months (in hundredths)	24.00%	60.00%	32.00%
12 months or more (in hundredths)	53.00%	20.00%	36.00%
Total primary default inventory (in hundredths)	100.00%	100.00%	100.00%
Primary claims received inventory included in ending default inventory	211	159	538
Percent of inventory in default for more than 36 consecutive months	20.00%	31.00%	36.00%