Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 448,611		$ 447,685
Fair value of contingent consideration	1,300	$ 1,500
Consideration paid in cash	$ 2,000	$ 3,300
Number of common stock issued	32,000	59,000
Common stock value related to contingent earnouts for previous acquisitions	$ 300	$ 500
Model Consulting, Inc. (Model),Pension Resource Group, Inc. (PRG),Cottonwood Group, Inc. (Cottonwood)[Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	988	6,865
Model Consulting, Inc. (Model),Pension Resource Group, Inc. (PRG),Cottonwood Group, Inc. (Cottonwood)[Member] | Financial Services [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	1,000
Model Consulting, Inc. (Model),Pension Resource Group, Inc. (PRG),Cottonwood Group, Inc. (Cottonwood)[Member] | Employee Services [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill		$ 6,900
Millimaki Eggert, L.L.P [Member]
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration	1,200
Millimaki Eggert, L.L.P [Member] | Contingent Purchase Price Liability Current [Member]
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration	500
Millimaki Eggert, L.L.P [Member] | Contingent Purchase Price Liability Non-current [Member]
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration	$ 700