Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Fair Value Of Assets And Liabilities Statement [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	$ 2,094,000
Payments to Acquire Businesses, Gross	109,384,000	$ 105,100,000
Recorded Earn-Out Payable	2,393,000
Other current assets	4,277,000
Fixed assets	649,000
Goodwill	78,664,000
Purchased customer accounts	44,135,000
Non-compete agreements	184,000
Total assets acquired	130,003,000
Other current liabilities	(4,004,000)
Deferred Tax Liabilities, Net	(3,230,000)
Total liabilities assumed	(7,234,000)
Net assets acquired	122,769,000
Maximum Potential Earn- Out Payable	11,864,000
SSAD [Member]
Fair Value Of Assets And Liabilities Statement [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	2,094,000
Other current assets	1,042,000
Fixed assets	307,000
Goodwill	22,321,000
Purchased customer accounts	13,069,000
Non-compete agreements	72,000
Total assets acquired	38,905,000
Other current liabilities	(1,686,000)
Deferred Tax Liabilities, Net	(3,230,000)
Total liabilities assumed	(4,916,000)
Net assets acquired	33,989,000
Morstan General Agency, Inc. [Member]
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	2,482,000
Fixed assets	300,000
Goodwill	49,954,000
Purchased customer accounts	26,775,000
Non-compete agreements	39,000
Total assets acquired	79,550,000
Other current liabilities	(1,415,000)
Deferred Tax Liabilities, Net	0
Total liabilities assumed	(1,415,000)
Net assets acquired	78,135,000
Other Acquisitions [Member]
Fair Value Of Assets And Liabilities Statement [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	0
Other current assets	753,000
Fixed assets	42,000
Goodwill	6,389,000
Purchased customer accounts	4,291,000
Non-compete agreements	73,000
Total assets acquired	11,548,000
Other current liabilities	(903,000)
Deferred Tax Liabilities, Net	0
Total liabilities assumed	(903,000)
Net assets acquired	10,645,000
Wholesale Brokerage
Fair Value Of Assets And Liabilities Statement [Line Items]
Goodwill	$ 49,978,000