Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income		$ 46.2	$ 56.4
Adjustments to reconcile net income to net cash provided by operating activities:
Asset impairments		0.0	0.5
Depreciation and amortization		22.0	19.8
Stock-based compensation		5.1	3.5
Loss on disposal of other assets		0.1	0.0
(Gain) loss on disposal of franchise		(0.1)	0.1
Deferred income taxes		8.2	5.2
(Increase) decrease (net of acquisitions and dispositions):
Accounts receivable, net		202.1	49.9
Inventories		(69.8)	(81.4)
Other assets		(6.8)	9.0
Increase (decrease) (net of acquisitions and dispositions):
Floor plan notes payable		(32.7)	34.6
Trade payables		(14.6)	(6.4)
Accrued liabilities		(49.4)	(14.5)
Other long-term liabilities and deferred revenue		11.4	0.5
Net cash provided by operating activities		121.7	77.2
Cash flows from investing activities:
Capital expenditures		(41.6)	(29.1)
Proceeds from sales of assets		0.2	0.4
Cash paid for other investments		(9.3)	(6.6)
Cash paid for acquisitions, net of cash acquired		(72.3)	0.0
Proceeds from sales of stores		4.7	0.0
Net cash used in investing activities		(118.3)	(35.3)
Cash flows from financing activities:
(Repayments) borrowings on floor plan notes payable, net: non-trade		(43.5)	43.5
Borrowings on lines of credit		430.0	570.0
Repayments on lines of credit		(375.0)	(625.0)
Principal payments on long-term debt and capital leases, scheduled		(6.5)	(6.2)
Principal payments on long-term debt and capital leases, other		0.0	(3.3)
Proceeds from issuance of long-term debt		17.2	0.0
Payments of debt issuance costs		(0.4)	0.0
Proceeds from issuance of common stock		2.6	2.3
Repurchase of common stock		(48.2)	(3.1)
Dividends paid		(7.0)	(6.7)
Net cash used in financing activities		(30.8)	(28.5)
(Decrease) increase in cash and cash equivalents		(27.4)	13.4
Cash and cash equivalents at beginning of period		84.0	31.6
Cash and cash equivalents at end of period		56.6	45.0
Supplemental disclosure of cash flow information:
Cash paid during the period for interest		31.5	37.9
Cash paid during the period for income taxes, net		1.3	0.2
Floor plan debt paid in connection with store disposals		0.0	4.8
Supplemental schedule of non-cash activities:
ROU assets obtained in exchange for lease liabilities	[1]	$ 1.8	$ 257.0

[1] Amounts for the three months ended March 31, 2019 include the transition adjustment for the adoption of Topic 842.