Goodwill and Other Intangible Assets Goodwill (Schedule of Consideration Paid and Net Assets Acquired, Business Combinations, 2019 Acquisitions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquisition consideration:
Cash, net of cash acquired and other	$ 24,971	$ 179,481	$ 6,684
Identifiable assets acquired and liabilities assumed:
Goodwill	1,243,034	$ 1,221,440	$ 1,100,400
2019 Acquisitions [Member]
Acquisition consideration:
Cash, net of cash acquired and other	176,400
Estimated fair value of contingent consideration and other liabilities	40,100
Total consideration transferred	216,500
Identifiable assets acquired and liabilities assumed:
Current assets, primarily composed of accounts receivable	92,600
Property and equipment, including finance leases and other long-term assets	56,100
Amortizing intangible assets	65,900
Current liabilities, including current portion of finance lease obligations and long-term debt	(89,000)
Long-term debt, including finance lease obligations	(2,400)
Deferred income taxes and other long-term liabilities	(27,500)
Total identifiable net assets	95,700
Goodwill	120,800
Total net assets acquired, including goodwill	$ 216,500