Consolidated Statements Of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues [Abstract]
Finance Charges Revenue	$ 1,176.8	$ 1,011.5	$ 874.3
Premiums earned	46.6	41.1	43.0
Other Income	62.4	57.4	51.9
Total revenue	1,285.8	1,110.0	969.2
Costs and expenses [Abstract]
Salaries and wages	167.8	140.1	126.5
General and administrative	55.7	55.5	48.2
Sales and marketing	67.7	58.4	49.4
Provision for credit losses	56.9	129.3	90.2
Interest	156.6	120.2	97.7
Provision for claims	26.0	22.7	26.0
Total costs and expenses	530.7	526.2	438.0
Income before provision for income taxes	755.1	583.8	531.2
Provision for income taxes	181.1	113.6	198.4
Net income	$ 574.0	$ 470.2	$ 332.8
Net income per share [Abstract]
Basic	$ 29.52	$ 24.12	$ 16.37
Diluted	$ 29.39	$ 24.04	$ 16.31
Weighted average Shares Outstanding [Abstract]
Basic	19,446,067	19,497,719	20,331,769
Diluted	19,532,312	19,558,936	20,410,116