Acquisitions (Aggregate purchase price) - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 442,624	$ 435,231
Clearview National Partners, L.L.C, Centric Insurance Agency and Lewis Birch & Richardo, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	6,865		$ 26,325
Employee Services [Member] | Clearview National Partners, L.L.C, Centric Insurance Agency and Lewis Birch & Richardo, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 6,900		17,100
Financial Services [Member] | Clearview National Partners, L.L.C, Centric Insurance Agency and Lewis Birch & Richardo, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill			$ 9,200