Goodwill - Changes in Carrying Value of Goodwill by Operating Segment (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 3,432,786
Goodwill of acquired businesses	80,432
Ending balance	$ 3,513,218
Document Period End Date	Mar. 31, 2019
Services
Goodwill [Roll Forward]
Beginning balance	$ 2,063,150
Goodwill of acquired businesses	55,117
Ending balance	2,118,267
National Programs
Goodwill [Roll Forward]
Beginning balance	926,206
Goodwill of acquired businesses	0
Ending balance	926,206
Wholesale Brokerage
Goodwill [Roll Forward]
Beginning balance	291,622
Goodwill of acquired businesses	6,063
Ending balance	297,685
Services
Goodwill [Roll Forward]
Beginning balance	151,808
Goodwill of acquired businesses	19,252
Ending balance	$ 171,060

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

No definition available.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

+ Details

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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