Finance Receivables - Aging Of Past Due Finance Receivables Including Non-Accrual Status Finance Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Past Due [Line Items]
Current	$ 7,324,346	$ 7,181,915
Total Past Due	248,601	229,901
Total finance receivables	7,572,947	7,411,816	$ 7,157,557	$ 7,008,801	$ 7,015,331
31-60 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	143,624	137,467
61-90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	54,379	50,098
Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	50,598	42,336
Retail
Financing Receivable, Past Due [Line Items]
Current	6,171,930	6,100,186
Total Past Due	244,498	228,015
Total finance receivables	6,416,428	6,328,201	6,140,600	5,982,211	5,991,471
Retail | 31-60 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	142,479	136,945
Retail | 61-90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	53,995	49,825
Retail | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	48,024	41,245
Wholesale
Financing Receivable, Past Due [Line Items]
Current	1,152,416	1,081,729
Total Past Due	4,103	1,886
Total finance receivables	1,156,519	1,083,615	$ 1,016,957	$ 1,026,590	$ 1,023,860
Wholesale | 31-60 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,145	522
Wholesale | 61-90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	384	273
Wholesale | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 2,574	$ 1,091