Goodwill and Other Intangible Assets (Schedule of Consideration Paid and Net Assets Acquired, Business Combinations) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Identifiable assets acquired and liabilities assumed:
Goodwill	$ 1,135,450		$ 995,874
Earn-Out Arrangements [Member]
Acquisition consideration:
Fair value of contingent consideration (earn-out liability)	89,614	$ 0
2017 Acquisitions [Member]
Acquisition consideration:
Cash	118,800
Total consideration transferred	208,400
Identifiable assets acquired and liabilities assumed:
Current assets, primarily composed of accounts receivable and $2.8 million of cash acquired	42,700
Cash acquired	2,800
Property and equipment	56,900
Amortizing intangible assets	26,800
Other long-term assets	500
Current liabilities, including current portion of capital lease obligations and long-term debt	(28,400)
Long-term debt, including capital lease obligations	(9,900)
Deferred income taxes	(15,500)
Total identifiable net assets	73,100
Goodwill	135,300
Total net assets acquired, including goodwill	208,400
2017 Acquisitions [Member] | Earn-Out Arrangements [Member]
Acquisition consideration:
Fair value of contingent consideration (earn-out liability)	$ 89,600