Acquisitions and Divestitures - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	14 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Nov. 02, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 2,128,776	$ 2,153,988		$ 956,153
Alliance Automotive Group [Member]
Business Acquisition [Line Items]
Trade accounts receivable	386,000		$ 380,000
Merchandise inventories	378,000		374,000
Prepaid expenses and other current assets	223,000		213,000
Intangible assets	813,000		727,000
Deferred tax assets	2,000		4,000
Property and equipment	92,000		93,000
Other assets	14,000		25,000
Total identifiable assets acquired	1,908,000		1,816,000
Current liabilities	(818,000)		(768,000)
Long-term debt	(769,000)		(769,000)
Pension and other post-retirement benefit liabilities	(14,000)		(14,000)
Deferred tax liabilities	(172,000)		(151,000)
Other long-term liabilities	(34,000)		(32,000)
Total liabilities assumed	(1,807,000)		(1,734,000)
Net identifiable assets acquired	101,000		82,000
Noncontrolling interests in subsidiaries	(37,000)		(38,000)
Goodwill	1,003,000		1,036,000
Net assets acquired	1,067,000		$ 1,080,000
Measurement Period Adjustments
Trade accounts receivable	6,000
Merchandise inventories	4,000
Prepaid expenses and other current assets	10,000
Intangible assets	86,000
Deferred tax assets	(2,000)
Property and equipment	(1,000)
Other assets	(11,000)
Total identifiable assets acquired	92,000
Current liabilities	(50,000)
Long-term debt	0
Pension and other post-retirement benefit liabilities	0
Deferred tax liabilities	(21,000)
Other long-term liabilities	(2,000)
Total liabilities assumed	(73,000)
Net identifiable assets acquired	19,000
Noncontrolling interests in subsidiaries	1,000
Goodwill	(33,000)
Net assets acquired	$ (13,000)