Loss Reserves - Delinquent Items (Details) - loan	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Insurance Loss Reserves [Abstract]
Percent of delinquency inventory subject to a Covid-19 forbearance plan (as a percent)	67.00%
Aging of the Primary Delinquent Inventory [Abstract]
3 months or less (in loans)	15,879		9,447	9,462
3 months or less (as a percent)	25.00%		32.00%	32.00%
4 - 11 months (in loans)	37,702		9,664	9,082
4 - 11 months (as a percent)	58.00%		32.00%	30.00%
12 months or more (in loans)	10,837		10,917	11,396
12 months or more (as a percent)	17.00%		36.00%	38.00%
Total primary delinquent inventory (in loans)	64,418	69,326	30,028	29,940	29,795	32,898
Total primary delinquent inventory (as a percent)	100.00%		100.00%	100.00%
Primary claims received inventory included in ending delinquent inventory (in loans)	172		538	557
Percent of 12 months or more delinquent inventory, delinquent for more than 36 months (as a percent)	32.00%		36.00%	36.00%