Stock and Stock-Based Incentive Plans Stock And Stock-Based Incentive Plans (Composition of Share-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense, before income taxes	$ 16,113	$ 11,769	$ 53,493	$ 73,096
Cost of sales
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense, before income taxes	963	584	2,266	2,998
Carmax Auto Finance Income
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense, before income taxes	895	663	2,563	2,314
Selling, general and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense, before income taxes	$ 14,255	$ 10,522	$ 48,664	$ 67,784