Acquisitions Accounted for Business Combinations (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	$ 14,366,000	$ 428,612,000
Note Payable		59,000
Net Assets Acquired	15,848,000	465,184,000
Arrowhead General Insurance Agency Superholding Corporation [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	(454,000)	423,858,000
Insurcorp & GGM Investments LLC [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	(834,000)	21,332,000
Richard W. Endlar Insurance Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	220,000
Texas Security General Insurance Agency Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	(107,000)
The Rollins Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	16,098,000
Other Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	925,000	19,994,000
2013 Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	14,384,000
Other Payable	(369,000)
Recorded Earn-out Payable	1,833,000
Net Assets Acquired	15,848,000
Maximum Potential Earn-Out Payable	4,748,000
2013 Acquisitions [Member] | Arrowhead General Insurance Agency Superholding Corporation [Member] | National Programs & Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition	Jan. 09, 2012
Other Payable	(454,000)
Net Assets Acquired	(454,000)
2013 Acquisitions [Member] | Insurcorp & GGM Investments LLC [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition	May 01, 2012
Recorded Earn-out Payable	(834,000)
Net Assets Acquired	(834,000)
2013 Acquisitions [Member] | Richard W. Endlar Insurance Agency, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition	May 01, 2012
Recorded Earn-out Payable	220,000
Net Assets Acquired	220,000
2013 Acquisitions [Member] | Texas Security General Insurance Agency Inc. [Member] | Wholesale Brokerage [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition	Sep. 01, 2012
Recorded Earn-out Payable	(107,000)
Net Assets Acquired	(107,000)
2013 Acquisitions [Member] | The Rollins Agency, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition	Jun. 01, 2013
Cash Paid	13,792,000
Other Payable	50,000
Recorded Earn-out Payable	2,256,000
Net Assets Acquired	16,098,000
Maximum Potential Earn-Out Payable	4,300,000
2013 Acquisitions [Member] | Other Acquisitions [Member] | Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	592,000
Other Payable	35,000
Recorded Earn-out Payable	298,000
Net Assets Acquired	925,000
Maximum Potential Earn-Out Payable	448,000
2012 Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid		428,612,000
Note Payable		59,000
Other Payable		23,594,000
Recorded Earn-out Payable		12,919,000
Net Assets Acquired		465,184,000
Maximum Potential Earn-Out Payable		32,235,000
2012 Acquisitions [Member] | Arrowhead General Insurance Agency Superholding Corporation [Member] | National Programs & Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition		Jan. 09, 2012
Cash Paid		397,531,000
Other Payable		22,694,000
Recorded Earn-out Payable		3,634,000
Net Assets Acquired		423,859,000
Maximum Potential Earn-Out Payable		5,000,000
2012 Acquisitions [Member] | Insurcorp & GGM Investments LLC [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Date of Acquisition		May 01, 2012
Cash Paid		15,500,000
Other Payable		900,000
Recorded Earn-out Payable		4,932,000
Net Assets Acquired		21,332,000
Maximum Potential Earn-Out Payable		17,000,000
2012 Acquisitions [Member] | Other Acquisitions [Member] | Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid		15,581,000
Note Payable		59,000
Recorded Earn-out Payable		4,353,000
Net Assets Acquired		19,993,000
Maximum Potential Earn-Out Payable		$ 10,235,000