Acquisitions Accounted for Business Combinations (Detail) (USD $)						3 Months Ended					3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Purchase Price Allocation Adjustments [Member]	Mar. 31, 2013 Arrowhead General Insurance Agency Superholding Corporation [Member]	Mar. 31, 2012 Arrowhead General Insurance Agency Superholding Corporation [Member]	Mar. 31, 2013 Arrowhead General Insurance Agency Superholding Corporation [Member] Purchase Price Allocation Adjustments [Member] National Programs & Services [Member]	Mar. 31, 2013 Other Acquisitions [Member]	Mar. 31, 2012 Other Acquisitions [Member]	Mar. 31, 2013 Other Acquisitions [Member] Purchase Price Allocation Adjustments [Member] Various [Member]	Mar. 31, 2013 Insurcorp & GGM Investments LLC [Member]	Mar. 31, 2013 Insurcorp & GGM Investments LLC [Member] Purchase Price Allocation Adjustments [Member] Retail [Member]	Mar. 31, 2013 Richard W. Endlar Insurance Agency, Inc. [Member]	Mar. 31, 2013 Richard W. Endlar Insurance Agency, Inc. [Member] Purchase Price Allocation Adjustments [Member] Retail [Member]	Mar. 31, 2013 Texas Security General Insurance Agency Inc. [Member]	Mar. 31, 2013 Texas Security General Insurance Agency Inc. [Member] Purchase Price Allocation Adjustments [Member] Wholesale Brokerage [Member]	Mar. 31, 2013 Business Combinations [Member]	Mar. 31, 2013 Business Combinations [Member] Arrowhead General Insurance Agency Superholding Corporation [Member] National Programs & Services [Member]	Mar. 31, 2013 Business Combinations [Member] Other Acquisitions [Member] Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition						Jan. 09, 2012					May 01, 2012		May 01, 2012		Sep. 01, 2012		Jan. 09, 2012
Cash Paid	$ 61,000	$ 401,247,000	$ 61,000						$ 61,000							$ 401,247,000	$ 397,531,000	$ 3,716,000
Note Payable
Other Payable	454,000	21,391,000	(454,000)			(454,000)										21,391,000	21,391,000
Recorded Earn-out Payable			(721,000)								(834,000)		220,000		(107,000)	4,714,000	3,634,000	1,080,000
Net Assets Acquired	(1,114,000)	427,352,000	(1,114,000)	(454,000)	422,556,000	(454,000)	61,000	4,796,000	61,000	(834,000)	(834,000)	220,000	220,000	(107,000)	(107,000)	427,352,000	422,556,000	4,796,000
Maximum Potential Earn-out Payable																$ 8,488,000	$ 5,000,000	$ 3,488,000