Loss Reserves - Delinquent Items (Details) - loan	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Aging of the Primary Delinquent Inventory [Abstract]
3 months or less (in loans)	6,948		11,542	15,879
4 - 11 months (in loans)	9,371		34,620	37,702
12 months or more (in loans)	21,060		11,548	10,837
Total primary delinquent inventory (in loans)	37,379	42,999	57,710	64,418	69,326	30,028
3 months or less (as a percent)	19.00%		20.00%	25.00%
4 - 11 months (as a percent)	25.00%		60.00%	58.00%
12 months or more (as a percent)	56.00%		20.00%	17.00%
Total primary delinquent inventory (as a percent)	100.00%		100.00%	100.00%
Primary claims received inventory included in ending delinquent inventory (in loans)	154		159	172
Percent of 12 months or more delinquent inventory, delinquent for more than 36 months (as a percent)	17.00%		31.00%	32.00%