Acquisitions Accounted for Business Combinations (Detail) (USD $)					12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended								12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Arrowhead General Insurance Agency Superholding Corporation	Dec. 31, 2012 Arrowhead General Insurance Agency Superholding Corporation National Programs & Services	Dec. 31, 2012 Insurcorp & GGM Investments LLC	Dec. 31, 2012 Insurcorp & GGM Investments LLC Retail	Dec. 31, 2012 Richard W. Endlar Insurance Agency, Inc.	Dec. 31, 2012 Richard W. Endlar Insurance Agency, Inc. Retail	Dec. 31, 2012 Texas Security General Insurance Agency Inc.	Dec. 31, 2012 Texas Security General Insurance Agency Inc. Wholesale Brokerage	Dec. 31, 2012 Behnke & Associates, Inc.	Dec. 31, 2012 Behnke & Associates, Inc. Retail	Dec. 31, 2012 Rowlands & Barranca Agency Inc.	Dec. 31, 2012 Rowlands & Barranca Agency Inc. Retail	Dec. 31, 2012 Other Acquisitions	Dec. 31, 2011 Other Acquisitions	Dec. 31, 2010 Other Acquisitions	Dec. 31, 2012 Other Acquisitions Various	Dec. 31, 2011 Other Acquisitions Various	Dec. 31, 2010 Other Acquisitions Various	Dec. 31, 2011 Balcos Insurance, Inc., Et Al	Dec. 31, 2011 Balcos Insurance, Inc., Et Al Retail	Dec. 31, 2011 Associated Insurance Service, Inc. et al. Retail	Dec. 31, 2011 United Benefit Services Insurance Agency LLC et al. Retail	Dec. 31, 2011 First Horizon Insurance Group, Inc. et al.	Dec. 31, 2011 First Horizon Insurance Group, Inc. et al. Retail	Dec. 31, 2011 Fitzharris Agency, Inc. et al.	Dec. 31, 2011 Fitzharris Agency, Inc. et al. Retail	Dec. 31, 2011 Corporate Benefit Consultants, LLC	Dec. 31, 2011 Corporate Benefit Consultants, LLC Retail	Dec. 31, 2011 Sitzmann, Morris & Lavis Insurance Agency, Inc. et al.	Dec. 31, 2011 Sitzmann, Morris & Lavis Insurance Agency, Inc. et al. Retail	Dec. 31, 2011 Snapper Shuler Kenner, Inc. et al.	Dec. 31, 2011 Snapper Shuler Kenner, Inc. et al. Retail	Dec. 31, 2011 Industry Consulting Group, Inc.	Dec. 31, 2011 Industry Consulting Group, Inc. National Programs & Services	Dec. 31, 2011 Colonial Claims Corporation et al.	Dec. 31, 2011 Colonial Claims Corporation et al. Services	Dec. 31, 2010 DiMartino Associates,Inc	Dec. 31, 2010 DiMartino Associates,Inc Retail	Dec. 31, 2010 Stone Insurance Agencies, et al.	Dec. 31, 2010 Stone Insurance Agencies, et al. Retail	Dec. 31, 2010 Crowe Paradis Holding Company,et al.	Dec. 31, 2010 Crowe Paradis Holding Company,et al. Services	Dec. 31, 2010 Thomas R Jones, Inc	Dec. 31, 2010 Thomas R Jones, Inc Retail
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition					Jan. 09, 2012		May 01, 2012		May 01, 2012		Sep. 01, 2012		Dec. 01, 2012		Dec. 01, 2012								Jan. 01, 2011	Jan. 01, 2011	Feb. 01, 2011		Apr. 30, 2011		May 01, 2011		Jun. 01, 2011		Nov. 01, 2011		Nov. 01, 2011		Nov. 01, 2011		Dec. 23, 2011		Mar. 01, 2010		May 01, 2010		Sep. 01, 2010		Oct. 01, 2010
Cash Paid	$ 483,933,000	$ 167,444,000	$ 158,636,000		$ 396,952,000		$ 15,500,000		$ 10,825,000		$ 14,506,000		$ 9,213,000		$ 8,745,000				$ 28,192,000	$ 25,295,000	$ 46,130,000		$ 8,611,000	$ 12,000,000	$ 14,283,000		$ 25,060,000		$ 6,159,000		$ 9,000,000		$ 40,460,000		$ 7,493,000		$ 9,133,000		$ 9,950,000		$ 7,047,000		$ 15,825,000		$ 75,000,000		$ 14,634,000
Note Payable	59,000	1,194,000	759,000																59,000	1,194,000	759,000
Other Payable	25,439,000			22,061,000	22,061,000		900,000				2,182,000								296,000
Recorded Earn-out Payable	21,479,000	30,525,000	25,090,000		3,290,000		4,944,000		2,598,000		2,124,000		1,126,000		2,401,000				4,996,000	6,168,000	12,899,000		1,595,000	1,575,000	2,590,000				888,000		2,038,000		6,228,000		1,318,000		3,877,000		4,248,000		3,402,000		124,000		8,665,000
Net Assets Acquired	530,910,000	199,163,000	184,485,000	422,303,000	422,303,000	21,344,000	21,344,000	13,423,000	13,423,000	18,812,000	18,812,000	10,339,000	10,339,000	11,146,000	11,146,000	33,543,000	32,657,000	59,788,000	33,543,000	32,657,000	59,788,000	10,206,000	10,206,000	13,575,000	16,873,000	25,060,000	25,060,000	7,047,000	7,047,000	11,038,000	11,038,000	46,688,000	46,688,000	8,811,000	8,811,000	13,010,000	13,010,000	14,198,000	14,198,000	10,449,000	10,449,000	15,949,000	15,949,000	83,665,000	83,665,000	14,634,000	14,634,000
Maximum Potential Earn-out Payable	$ 56,170,000	$ 78,207,000	$ 54,305,000		$ 5,000,000		$ 17,000,000		$ 5,500,000		$ 7,200,000		$ 3,321,000		$ 4,000,000				$ 14,149,000	$ 12,865,000	$ 30,668,000		$ 5,766,000	$ 6,000,000	$ 8,442,000				$ 3,832,000		$ 4,520,000		$ 19,000,000		$ 3,988,000		$ 5,794,000		$ 8,000,000		$ 5,637,000		$ 3,000,000		$ 15,000,000