Acquisitions Accounted for Business Combinations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	$ 408,072	$ 483,933	$ 167,444
Note Payable		59	1,194
Other Payable			30,525
Net Assets Acquired	413,715	530,910	199,163
Maximum Potential Earn-out Payable			78,207
Arrowhead General Insurance Agency Superholding Corporation [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		422,303
Insurcorp & GGM Investments LLC [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		21,344
Richard W. Endlar Insurance Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		13,423
Texas Security General Insurance Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		18,812
The Rollins Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	16,163
Beecher Carlson Holdings, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	364,256
Other Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	12,799	33,543	32,657
Other Acquisitions [Member] | Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid			25,295
Note Payable			1,194
Other Payable			6,168
Net Assets Acquired			32,657
Maximum Potential Earn-out Payable			12,865
Behnke & Associates, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		10,339
Rowlands & Barranca Agency, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired		11,146
ICA, Inc.[Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	20,497
Balcos Insurance, Inc., Et Al [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			10,206
Balcos Insurance, Inc., Et Al [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid			8,611
Other Payable			1,595
Net Assets Acquired			10,206
Maximum Potential Earn-out Payable			5,766
Associated Insurance Service, Inc. et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Jan. 01, 2011
Cash Paid			12,000
Other Payable			1,575
Net Assets Acquired			13,575
Maximum Potential Earn-out Payable			6,000
United Benefit Services Insurance Agency LLC et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Feb. 01, 2011
Cash Paid			14,283
Other Payable			2,590
Net Assets Acquired			16,873
Maximum Potential Earn-out Payable			8,442
First Horizon Insurance Group, Inc. et al. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			25,060
First Horizon Insurance Group, Inc. et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Apr. 30, 2011
Cash Paid			25,060
Net Assets Acquired			25,060
Fitzharris Agency, Inc. et al. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			7,047
Fitzharris Agency, Inc. et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			May 01, 2011
Cash Paid			6,159
Other Payable			888
Net Assets Acquired			7,047
Maximum Potential Earn-out Payable			3,832
Corporate Benefit Consultants, LLC [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			11,038
Corporate Benefit Consultants, LLC [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Jun. 01, 2011
Cash Paid			9,000
Other Payable			2,038
Net Assets Acquired			11,038
Maximum Potential Earn-out Payable			4,520
Sitzmann, Morris & Lavis Insurance Agency, Inc. et al. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			46,688
Sitzmann, Morris & Lavis Insurance Agency, Inc. et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Nov. 01, 2011
Cash Paid			40,460
Other Payable			6,228
Net Assets Acquired			46,688
Maximum Potential Earn-out Payable			19,000
Snapper Shuler Kenner, Inc. et al. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			8,811
Snapper Shuler Kenner, Inc. et al. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Nov. 01, 2011
Cash Paid			7,493
Other Payable			1,318
Net Assets Acquired			8,811
Maximum Potential Earn-out Payable			3,988
Industry Consulting Group, Inc. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			13,010
Industry Consulting Group, Inc. [Member] | National Programs & Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid			9,133
Other Payable			3,877
Net Assets Acquired			13,010
Maximum Potential Earn-out Payable			5,794
Colonial Claims Corporation et al. [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired			14,198
Colonial Claims Corporation et al. [Member] | Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition			Dec. 23, 2011
Cash Paid			9,950
Other Payable			4,248
Net Assets Acquired			14,198
Maximum Potential Earn-out Payable			8,000
2013 Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	408,072
Other Payable	552
Recorded Earn-out Payable	5,091
Net Assets Acquired	413,715
Maximum Potential Earn-out Payable	16,768
2013 Acquisitions [Member] | The Rollins Agency, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition	Jun. 01, 2013
Cash Paid	13,792
Other Payable	50
Recorded Earn-out Payable	2,321
Net Assets Acquired	16,163
Maximum Potential Earn-out Payable	4,300
2013 Acquisitions [Member] | Beecher Carlson Holdings, Inc. [Member] | Retail And National Programs [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition	Jul. 01, 2013
Cash Paid	364,256
Other Payable
Recorded Earn-out Payable
Net Assets Acquired	364,256
Maximum Potential Earn-out Payable
2013 Acquisitions [Member] | Other Acquisitions [Member] | Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	10,254
Other Payable	502
Recorded Earn-out Payable	2,043
Net Assets Acquired	12,799
Maximum Potential Earn-out Payable	7,468
2013 Acquisitions [Member] | ICA, Inc.[Member] | Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition	Dec. 31, 2013
Cash Paid	19,770
Other Payable
Recorded Earn-out Payable	727
Net Assets Acquired	20,497
Maximum Potential Earn-out Payable	5,000
2012 Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid		483,933
Note Payable		59
Other Payable		25,439
Recorded Earn-out Payable		21,479
Net Assets Acquired		530,910
Maximum Potential Earn-out Payable		56,170
2012 Acquisitions [Member] | Arrowhead General Insurance Agency Superholding Corporation [Member] | National Programs & Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		Jan. 09, 2012
Cash Paid		396,952
Other Payable		22,061
Recorded Earn-out Payable		3,290
Net Assets Acquired		422,303
Maximum Potential Earn-out Payable		5,000
2012 Acquisitions [Member] | Insurcorp & GGM Investments LLC [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		May 01, 2012
Cash Paid		15,500
Other Payable		900
Recorded Earn-out Payable		4,944
Net Assets Acquired		21,344
Maximum Potential Earn-out Payable		17,000
2012 Acquisitions [Member] | Richard W. Endlar Insurance Agency, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		May 01, 2012
Cash Paid		10,825
Recorded Earn-out Payable		2,598
Net Assets Acquired		13,423
Maximum Potential Earn-out Payable		5,500
2012 Acquisitions [Member] | Texas Security General Insurance Agency, Inc. [Member] | Wholesale Brokerage [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		Sep. 01, 2012
Cash Paid		14,506
Other Payable		2,182
Recorded Earn-out Payable		2,124
Net Assets Acquired		18,812
Maximum Potential Earn-out Payable		7,200
2012 Acquisitions [Member] | Other Acquisitions [Member] | Various [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid		28,192
Note Payable		59
Other Payable		296
Recorded Earn-out Payable		4,996
Net Assets Acquired		33,543
Maximum Potential Earn-out Payable		14,149
2012 Acquisitions [Member] | Behnke & Associates, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		Dec. 01, 2012
Cash Paid		9,213
Recorded Earn-out Payable		1,126
Net Assets Acquired		10,339
Maximum Potential Earn-out Payable		3,321
2012 Acquisitions [Member] | Rowlands & Barranca Agency, Inc. [Member] | Retail [Member]
Business Combination, Separately Recognized Transactions [Line Items]
2013 Date of Acquisition		Dec. 01, 2012
Cash Paid		8,745
Recorded Earn-out Payable		2,401
Net Assets Acquired		11,146
Maximum Potential Earn-out Payable		$ 4,000