Consolidated Statements Of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues [Abstract]
Finance charges	$ 1,011.5	$ 874.3	$ 730.5
Premiums earned	41.1	43.0	48.2
Other Income	57.4	51.9	46.6
Total revenue	1,110.0	969.2	825.3
Costs and expenses [Abstract]
Salaries and wages	140.1	126.5	116.4
General and administrative	55.5	48.2	37.8
Sales and marketing	58.4	49.4	45.9
Provision for credit losses	129.3	90.2	41.5
Interest	120.2	97.7	76.0
Provision for claims	22.7	26.0	33.2
Total costs and expenses	526.2	438.0	350.8
Income before provision for income taxes	583.8	531.2	474.5
Provision for income taxes	113.6	198.4	174.8
Net income	$ 470.2	$ 332.8	$ 299.7
Net income per share [Abstract]
Basic	$ 24.12	$ 16.37	$ 14.35
Diluted	$ 24.04	$ 16.31	$ 14.28
Weighted average Shares Outstanding [Abstract]
Basic	19,497,719	20,331,769	20,891,695
Diluted	19,558,936	20,410,116	20,980,753