Business Combinations - Net Asset Acquired (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	Oct. 01, 2020	Dec. 31, 2018
Net assets acquired:
Goodwill		$ 817,600	$ 811,400	$ 865,900	$ 817,600	$ 487,200
Adjustments
Goodwill		$ 400	38,400
AXC
Net assets acquired:
Identifiable intangible assets	$ 256,400		256,400
Goodwill	287,900		287,500
Property, plant and equipment	34,200		34,200
Other net assets	53,100		53,100
Liabilities	(31,900)		(31,500)
Net assets acquired	599,700		$ 599,700
Adjustments
Goodwill	400
Liabilities	(400)
Net assets acquired	$ 0