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Business Combinations - Acquisition Method for Recording Business Combinations (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2017
Construction Risk Solutions, LLC [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 01, 2017
Hill, Chesson And Woody [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 01, 2017
Presidio Group, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 01, 2017
Nine Other Acquisitions [Member]
Business Acquisition [Line Items]
Effective Year of Acquisition	2017

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- Definition

Business acquisition effective date of acquisition year.

+ References

No definition available.

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- Definition

Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=73531572&loc=d3e845-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Acquisition Date
-URI http://asc.fasb.org/extlink&oid=6919109

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73531572&loc=d3e848-128460

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463

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- Definition

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.

+ References

No definition available.

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