Goodwill and Other Intangible Assets - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Acquisition consideration:
Cash, net of cash acquired	$ 604,907	$ 11,251
Identifiable assets acquired and liabilities assumed:
Goodwill	1,338,597		$ 1,243,034
2021 Acquisitions
Acquisition consideration:
Cash, net of cash acquired	604,800
Estimated fair value of contingent consideration	40,100
Total consideration transferred	644,900
Identifiable assets acquired and liabilities assumed:
Current assets, primarily accounts receivable	219,200
Long-term assets, primarily property and equipment and operating lease assets	187,500
Amortizing intangible assets	367,200
Current liabilities, including current portion of operating lease liabilities	(145,400)
Long-term liabilities, primarily operating lease liabilities and deferred income taxes	(79,000)
Total identifiable net assets	549,500
Goodwill	95,400
Total net assets acquired, including goodwill	$ 644,900