Goodwill - Changes in Carrying Value of Goodwill by Operating Segment (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2015 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 2,460,611
Goodwill of acquired businesses	101,509
Goodwill disposed of relating to sales of businesses	(2,238)
Ending balance	2,559,882
Retail
Goodwill [Roll Forward]
Beginning balance	1,231,869
Goodwill of acquired businesses	80,533
Goodwill disposed of relating to sales of businesses	0
Ending balance	1,312,402
National Programs
Goodwill [Roll Forward]
Beginning balance	886,095
Goodwill of acquired businesses	18,009
Goodwill disposed of relating to sales of businesses	(2,238)
Ending balance	901,866
Wholesale Brokerage
Goodwill [Roll Forward]
Beginning balance	222,356
Goodwill of acquired businesses	2,967
Goodwill disposed of relating to sales of businesses	0
Ending balance	225,323
Services
Goodwill [Roll Forward]
Beginning balance	120,291
Goodwill of acquired businesses	0
Goodwill disposed of relating to sales of businesses	0
Ending balance	$ 120,291

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.

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=64834752&loc=SL49117168-202975

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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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- Definition

Amount of divestiture 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

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