Business Combinations - Acquisition Method for Recording Business Combinations (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014
Benefit Development Group, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Feb. 01, 2014
Kent, Kent & Tingle [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Feb. 01, 2014
L&R Benefits, LLC [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Mar. 01, 2014
Spataro Insurance Agency, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Mar. 01, 2014
Tudor Risk Services, LLC [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Mar. 01, 2014
American Wholesalers Underwriting Ltd [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Apr. 01, 2014
Mike Henry Insurance Brokers Limited [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Apr. 01, 2014
Oval Group of Companies (OGC) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Apr. 01, 2014
Heritage Insurance Management Limited (HIM) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	May 01, 2014
MGA Insurance Group (MGA) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	May 01, 2014
Shilling Limited [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	May 01, 2014
Sunderland Insurance Services, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	May 01, 2014
Plus Companies, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jun. 01, 2014
Tri-State General Insurance Agency, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jun. 01, 2014
Crombie/OAMPS (CO) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jun. 16, 2014
Foundation Strategies, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jul. 01, 2014
Insurance Point, LLC (IPL) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jul. 01, 2014
Trip Mate, Inc. (TMI) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jul. 01, 2014
Noraxis Capital Corporation (NCC) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jul. 02, 2014
Cowles & Connell (CC) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Aug. 01, 2014
Denman Consulting Services [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Aug. 01, 2014
Minvielle & Chastanet Insurance Brokers [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Aug. 08, 2014
Baker Tilly Financial Management Limited [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Aug. 29, 2014
Benfield Group [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Sep. 01, 2014
Everett James, Inc. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Sep. 01, 2014
Hagedorn & Company [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Sep. 01, 2014
Parmia Pty Ltd. [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Sep. 01, 2014
Bennett and Shade Company [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Oct. 01, 2014
Insurance Associates Inc [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Oct. 01, 2014
Forker Company [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Oct. 31, 2014
Discovery Benefit Solutions Inc [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Nov. 01, 2014
Miller Harrison Insurance Services [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Nov. 01, 2014
SGB-NIA Insurance Brokers (SGB) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Nov. 01, 2014
Titan Group LLC [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Nov. 01, 2014
Instrat Insurance Brokers [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Dec. 01, 2014
O Gorman & Young Incorporated (OGY) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Dec. 01, 2014
Independent Benefit Services, Inc. (IBS) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Dec. 01, 2014
Affinity Marketing Group [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Dec. 01, 2014
Blue Holdings Group of Companies [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Dec. 05, 2014