Business Acquisition - Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill	$ 1,126,843	$ 914,520
Goodwill, Acquired During Period	217,608
Goodwill, Foreign Currency Translation Gain (Loss)	(5,285)
Domestic Segment
Goodwill [Line Items]
Goodwill	971,235	854,188
Goodwill, Acquired During Period	117,047
Goodwill, Foreign Currency Translation Gain (Loss)	0
International Segment [Member]
Goodwill [Line Items]
Goodwill	155,608	$ 60,332
Goodwill, Acquired During Period	100,561
Goodwill, Foreign Currency Translation Gain (Loss)	$ (5,285)