Business Combinations - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 Y	Mar. 31, 2012 Y
Business Acquisition [Line Items]
Average annual operating profit earned period, minimum (years)	1	1
Average annual operating profit earned period, maximum (years)	3	3
Aggregate purchase price of acquisitions	$ 1,071,000	$ 559,241,000
Cash payments for acquisitions	61,000	401,247,000
Net additional consideration paid as note payable	454,000	21,391,000
Assumption of liabilities	43,000	131,889,000
Recorded earn-out payable	(721,000)	4,714,000
Total goodwill	323,044,000
Goodwill currently deductible for income tax purposes	3,226,000
Goodwill currently non-deductible for income tax purposes	315,104,000
Goodwill related to the recorded earn-out payables	4,714,000
Total revenues related to acquisitions		27,712,000
Income before income taxes related to acquisitions		362,000
Maximum future contingency payments related to acquisitions	147,631,000
Percentage recognition by acquirer of fair value of acquired assets	100.00%
Estimated acquisition earn-out payables	49,469,000	51,908,000
Other Non-Current Liability [Member]
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	33,688,000	43,126,000
Accounts Payable [Member]
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	15,781,000	8,782,000
Purchased customer accounts [Member]
Business Acquisition [Line Items]
Weighted average life (years)	15 years
Non-compete agreements [Member]
Business Acquisition [Line Items]
Weighted average life (years)	5 years
Subsequent to January 1, 2009 [Member]
Business Acquisition [Line Items]
Maximum future contingency payments related to acquisitions	147,631,000
Future earnings of acquired entities, term basis of potential earn-out obligations, minimum (years)	1
Future earnings of acquired entities, term basis of potential earn-out obligations, maximum (years)	3
Asset Acquisitions [Member]
Business Acquisition [Line Items]
Number of acquisitions	0	2
Stock Acquisitions [Member]
Business Acquisition [Line Items]
Number of acquisitions		1
Retail [Member]
Business Acquisition [Line Items]
Goodwill assigned	2,088,000
National Programs Divisions [Member]
Business Acquisition [Line Items]
Goodwill assigned	253,901,000
Wholesale Brokerage Divisions [Member]
Business Acquisition [Line Items]
Goodwill assigned	811,000
Services [Member]
Business Acquisition [Line Items]
Goodwill assigned	66,244,000
Prior to January 1, 2009 [Member]
Business Acquisition [Line Items]
Cash payments for acquisitions	626,000	2,907,000
Additional net consideration paid allocated to goodwill	626,000	2,907,000
Net additional consideration paid as note payable	$ 626,000