For contingent consideration arrangements recognized in connection with a business combination, this element represents an estimate of the high-end of the potential range (undiscounted) of the consideration which may be paid.

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For contingent consideration arrangements and indemnification assets recognized in connection with a business combination, this element represents an estimate of the low-end of the potential range (undiscounted) of the consideration which may be paid.

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Value of input used to measure contingent consideration liability from business combination.

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Fair value of obligations measured on a recurring basis.

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Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Fair Value of Financial Instruments (Acquisition-Related Contingent Consideration and Other Liabilities) (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, net increase (decrease), measurement period adjustments			$ 100,000
All Acquisitions [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low	$ 17,000,000		17,000,000
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high	$ 189,000,000		$ 189,000,000
Discount Rate \| Minimum
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.120		0.120
Discount Rate \| Maximum
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.235		0.235
Discount Rate \| Weighted Average
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.130		0.130
Earn-Out Liabilities
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	$ 119,800,000		$ 119,800,000		$ 135,200,000
Acquisition-related contingent consideration liabilities, additions from new business combinations	40,100,000	$ 7,200,000	40,100,000	$ 7,200,000
Acquisition-related contingent consideration liabilities, net increase (decrease), measurement period adjustments	0		0	1,100,000
Acquisition-related contingent consideration liabilities, net increase (decrease), fair value adjustments, expense (income)	(8,900,000)		(9,300,000)	1,700,000
Acquisition-related contingent consideration liabilities, payments	46,200,000	$ 50,400,000	46,200,000	$ 50,400,000
Earn-Out Liabilities \| Other Current Liabilities
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	58,900,000		58,900,000		48,100,000
Earn-Out Liabilities \| Mandatorily Redeemable Stock
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	16,800,000		16,800,000		$ 18,800,000
Acquisition-related contingent consideration liabilities, payments	$ 2,100,000		$ 2,100,000