Consolidated Statements Of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues [Abstract]
Finance Charges Revenue	$ 1,369.4	$ 1,176.8	$ 1,011.5
Premiums earned	51.0	46.6	41.1
Other Income	68.6	62.4	57.4
Total revenue	1,489.0	1,285.8	1,110.0
Costs and expenses [Abstract]
Salaries and wages	193.3	167.8	140.1
General and administrative	65.1	55.7	55.5
Sales and marketing	70.2	67.7	58.4
Provision for credit losses	76.4	56.9	129.3
Interest	196.2	156.6	120.2
Provision for claims	30.1	26.0	22.7
Loss on extinguishment of debt	1.8	0.0	0.0
Total costs and expenses	633.1	530.7	526.2
Income before provision for income taxes	855.9	755.1	583.8
Provision for income taxes	199.8	181.1	113.6
Net income	$ 656.1	$ 574.0	$ 470.2
Net income per share [Abstract]
Basic	$ 34.71	$ 29.52	$ 24.12
Diluted	$ 34.57	$ 29.39	$ 24.04
Weighted average Shares Outstanding [Abstract]
Basic	18,900,256	19,446,067	19,497,719
Diluted	18,976,560	19,532,312	19,558,936