Business Combinations - Additions, Payments, and Net Changes, as well as Interest Expense Accretion on Estimated Acquisition Earn-Out Payables (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition Cost- Note Payable	$ 492
Beginning balance	78,387	$ 75,283	$ 43,058
Additions to estimated acquisition earn-out payables	4,462	36,899	34,356
Payments for estimated acquisition earn-out payables	28,213	36,798	12,069
Subtotal	54,636	75,384	65,345
Net change in earnings from estimated acquisition earn-out payables:
Change in fair value on estimated acquisition earn-out payables	(6,338)	(13)	(7,375)
Interest expense accretion	2,847	2,990	2,563
Net change in earnings from estimated acquisition earn-out payables	9,185	3,003	9,938
Ending balance	63,821	$ 78,387	$ 75,283
Services | Social Security Advocates for the Disabled LLC [Member]
Business Acquisition [Line Items]
Business Acquisition Cost- Note Payable	492
Wholesale Brokerage [Member] | Morstan General Agency, Inc [Member]
Business Acquisition [Line Items]
Business Acquisition Cost- Note Payable	0
Various [Member] | Other Acquisitions [Member]
Business Acquisition [Line Items]
Business Acquisition Cost- Note Payable	$ 0