Discontinued Operations and Divestitures - Additional Information (Detail) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) Office	Sep. 30, 2017 Office	Dec. 31, 2015 Business
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of business divestiture | Office	0	0
Financial Services [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number Of Businesses Sold | Business			2
Benefits and Insurance Services Practice Group [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain from the sale of its individual wealth management business | $	$ 0.7