Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 385,292,000	$ 373,117,000	$ 320,761,000	$ 335,402,000
Goodwill impairment loss	0	0	0
Amortization of intangible assets	2,932,000	2,522,000	$ 5,821,000
Financial Advisory Segment [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill	320,751,000	308,576,000
Asset Management Segment [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 64,541,000	$ 64,541,000