Business Combinations - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) acquisition customer_account	Mar. 31, 2015 USD ($) acquisition	Jan. 01, 2016 USD ($)	Jan. 01, 2015 USD ($)
Business Acquisition [Line Items]
Number of acquisitions | acquisition	3	3
Aggregate purchase price of acquisitions	$ 1,074,754
Payments to Acquire Businesses, Gross	42,697,000	$ 36,200,000
Goodwill assigned	28,952,000
Goodwill currently deductible for income tax purposes	7,023,000
Goodwill currently non-deductible for income tax purposes	21,323,000
Goodwill related to the recorded earn-out payables	606,000
Total revenues related to acquisitions	2,527,000
Income before income taxes related to acquisitions	570,000
Estimated acquisition earn-out payables	69,095,000	$ 77,709,000	$ 78,387,000	$ 75,283,000
Accounts payable
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	$ 23,700,000
Purchased customer accounts
Business Acquisition [Line Items]
Weighted average life (years)	15 years
Non-compete agreements
Business Acquisition [Line Items]
Weighted average life (years)	5 years
Services
Business Acquisition [Line Items]
Goodwill assigned	$ 6,704,000
National Programs
Business Acquisition [Line Items]
Goodwill assigned	(70,000)
Wholesale Brokerage
Business Acquisition [Line Items]
Goodwill assigned	24,000
Services [Member]
Business Acquisition [Line Items]
Goodwill assigned	22,294,000
Other non-current liability
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	$ 45,400,000
Business Combinations - Asset Deals [Member]
Business Acquisition [Line Items]
Number of acquisitions | acquisition	2
Business Combinations - Stock Deals [Member]
Business Acquisition [Line Items]
Number of acquisitions | customer_account	1