Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Restricted Cash and Cash Equivalents	$ 34,559	$ 34,680
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	35,814	33,939
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
DEPRECIATION AND AMORTIZATION EXPENSE	16,342	13,606
Deferred income taxes	2,675	5,503
ASSET IMPAIRMENTS	0
Stock-based compensation	5,642	6,074
Amortization of debt discount and issue costs	650	912
Gain (Loss) on Disposition of Assets	(516)	(280)
Other	(6)	(871)
Changes in operating assets and liabilities, net of effects of acquisitions and dispositions:
Accounts payable and accrued expenses	65,200	9,164
Accounts and notes receivable	12,727	21,508
Inventories	7,153	(74,254)
Contracts-in-transit and vehicle receivables	11,237	56,140
Prepaid expenses and other assets	(12,548)	1,066
Floorplan notes payable - manufacturer affiliates	5,067	(3,126)
Deferred revenues	(655)	(164)
Net cash provided by operating activities	148,782	69,217
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash paid in acquisitions, net of cash received	(71,499)	(95)
Proceeds from disposition of franchises, property and equipment	2,940	2,207
Purchases of property and equipment, including real estate	(47,948)	(46,451)
Other	140	2,459
Net cash used in investing activities	(116,367)	(41,880)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings on credit facility - Floorplan Line	1,656,192	1,594,371
Repayments on credit facility - Floorplan Line	(1,702,447)	(1,598,291)
Borrowings on credit facility - acquisition line	66,945	15,000
Repayments on credit facility - acquisition line	(66,444)	(15,000)
Borrowings on other debt	65,614	0
Principal payments on other debt	(40,078)	(232)
Borrowings Of Long Term Debt Related To Real Estate Loans, Net of Debt Issue Costs	46,835	0
Principal payments of long-term debt related to real estate loans	(37,819)	(6,831)
Net Issuance of Common and Treasury Shares to Employee Stock Compensation Plans	(1,638)	(1,030)
Repurchases of common stock, amounts based on settlement date	(9,199)	0
Dividends paid	(5,495)	(5,150)
Net cash used in financing activities	(27,534)	(17,163)
Effect of Exchange Rate on Cash and Cash Equivalents	47	260
Cash, cash equivalents, and restricted cash period increase (decrease)	4,928	10,434
CASH AND CASH EQUIVALENTS, beginning of period	28,787	24,246
CASH AND CASH EQUIVALENTS, end of period	33,090
SUPPLEMENTAL CASH FLOW INFORMATION:
Purchases of property and equipment, including real estate, accrued in accounts payable and accrued expenses	$ 6,066	$ 7,287