Fair Value of Financial Instruments (Acquisition-Related Contingent Consideration) (Narrative) (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low	$ 41,000,000
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high	$ 196,000,000
Acquisition-related contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited	there is no maximum payment amount
Earn-Out Liabilities [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	$ 140,500,000		$ 118,100,000
Acquisition-related contingent consideration liabilities, additions from new business combinations	15,200,000	$ 1,500,000
Acquisition-related contingent consideration liabilities, net increase (decrease), fair value adjustments, expense (income)	7,200,000
Acquisition-related contingent consideration liabilities, net increase (decrease), measurement period adjustments		2,700,000
Acquisition-related contingent consideration liabilities, payments	0	$ 0
Earn-Out Liabilities [Member] \| Other Current Liabilities [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	$ 30,800,000		$ 29,600,000

For contingent consideration arrangements recognized in connection with a business combination, if the maximum (undiscounted) potential outcome is limitless, this element represents a statement of that fact.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of obligations measured on a recurring basis.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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-Paragraph 2
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Amount of gain (loss) recognized on the income statement for 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 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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460

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-Publisher FASB
-Name Accounting Standards Codification
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