Acquisitions (Fourth Quarter 2015) - Additional Information (Detail) - Participant		12 Months Ended
	Oct. 01, 2015	Dec. 31, 2016
Pension Resource Group Inc [Member]
Business Acquisition, Contingent Consideration [Line Items]
Acquired entity, name		Pension Resource Group, Inc
Effective date of acquisition		Oct. 01, 2015
Pension Resource Group Inc [Member] | Minimum [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of clients of acquired entity	500
Pension Resource Group Inc [Member] | Maximum [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of clients of acquired entity	60,000
Cottonwood [Member] | Benefit and Insurance Services Practice Group [Member]
Business Acquisition, Contingent Consideration [Line Items]
Acquired entity, name		Cottonwood Group, Inc
Effective date of acquisition		Dec. 01, 2015