Loss Reserves - Delinquent Items (Details) - loan	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Aging of the Primary Delinquent Inventory [Abstract]
3 months or less (in loans)	9,462		9,829	9,484
3 months or less (as a percent)	32.00%		30.00%	28.00%
4 - 11 months (in loans)	9,082		9,655	9,564
4 - 11 months (as a percent)	30.00%		29.00%	29.00%
12 months or more (in loans)	11,396		13,414	14,350
12 months or more (as a percent)	38.00%		41.00%	43.00%
Total primary delinquent inventory (in loans)	29,940	29,795	32,898	33,398	36,037	46,556
Total primary delinquent inventory (as a percent)	100.00%		100.00%	100.00%
Primary claims received inventory included in ending delinquent inventory (in loans)	557		809	766
Percent of 12 months or more delinquent inventory, delinquent for more than 36 months (as a percent)	36.00%		38.00%	39.00%