Business Combinations - Additions, Payments, and Net Changes, as well as Interest Expense Accretion on Estimated Acquisition Earn-Out Payables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Combinations [Abstract]
Beginning balance	$ 258,943	$ 161,513	$ 89,924
Additions to estimated acquisition earn-out payables from new acquisitions	75,761	131,397	82,872
Payments for estimated acquisition earn-out payables	(83,581)	(29,509)	(9,917)
Subtotal	251,123	263,401	162,879
Net change in earnings from estimated acquisition earn-out payables:
Change in fair value on estimated acquisition earn-out payables	34,209	(11,814)	(7,298)
Interest expense accretion	6,236	7,356	5,932
Net change in earnings from estimated acquisition earn- out payables	40,445	(4,458)	(1,366)
Foreign currency translation adjustments during the year	(521)	0	0
Ending balance	$ 291,047	$ 258,943	$ 161,513