Business Combinations - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Y	Jun. 30, 2012 Y	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Jan. 09, 2012
Business Acquisition [Line Items]
Aggregate purchase price of acquisitions	$ 17,865,000	$ 599,122,000	$ 17,865,000	$ 599,122,000
Cash payment for acquisition			14,366,000	428,612,000
Other payables for acquisition			85,000	23,594,000
Assumption of liabilities			860,000	133,938,000
Recorded earn-out payable			2,554,000	12,919,000
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	1,115,000		1,115,000
Cash payments for acquisitions	18,000		18,000
Net consideration paid as other note payable	454,000		454,000
Assumption of liabilities	42,000		42,000
Recorded earn-out payable	(721,000)		(721,000)
Total goodwill	10,687,000	349,561,000	10,687,000	349,561,000
Goodwill currently deductible for income tax purposes	9,308,000	19,909,000	9,308,000	19,909,000
Goodwill currently non-deductible for income tax purposes	(454,000)	316,733,000	(454,000)	316,733,000
Goodwill related to the recorded earn-out payables	1,833,000	12,919,000	1,833,000	12,919,000
Total revenues related to acquisitions	627,000	30,554,000	627,000	58,266,000
Income (loss) before income taxes related to acquisitions	142,000	(814,000)	142,000	(452,000)
Net additional consideration paid as note payable		59,000		59,000
Maximum future contingency payments related to acquisitions	135,199,000		135,199,000
Percentage recognition by acquirer of fair value of acquired assets			100.00%
Estimated acquisition earn-out payables	48,918,000	57,997,000	48,918,000	57,997,000	49,469,000	52,987,000	51,908,000	47,715,000
Other Non-Current Liability [Member]
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	34,463,000	41,315,000	34,463,000	41,315,000
Accounts Payable [Member]
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	14,455,000	16,682,000	14,455,000	16,682,000
Subsequent to January 1, 2009 [Member]
Business Acquisition [Line Items]
Maximum future contingency payments related to acquisitions	135,199,000		135,199,000
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
Retail [Member]
Business Acquisition [Line Items]
Goodwill assigned	11,984,000	26,976,000	11,984,000	26,976,000
National Programs Divisions [Member]
Business Acquisition [Line Items]
Goodwill assigned	(454,000)	252,761,000	(454,000)	252,761,000
Wholesale Brokerage Divisions [Member]
Business Acquisition [Line Items]
Goodwill assigned	(843,000)	811,000	(843,000)	811,000
Services [Member]
Business Acquisition [Line Items]
Goodwill assigned		69,013,000		69,013,000
Prior to January 1, 2009 [Member]
Business Acquisition [Line Items]
Cash payment for acquisition			627,000	2,907,000
Net additional consideration paid as note payable	627,000		627,000
Additional net consideration paid allocated to goodwill			$ 627,000	$ 2,907,000
Purchased customer accounts [Member]
Business Acquisition [Line Items]
Weighted average life (years)			15 years	15 years
Non-compete agreements [Member]
Business Acquisition [Line Items]
Weighted average life (years)			5 years	5 years
Asset Acquisitions [Member]
Business Acquisition [Line Items]
Number of acquisitions			2	7
Stock Acquisitions [Member]
Business Acquisition [Line Items]
Number of acquisitions				1