Segment Reporting - Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Advisory fees	$ 58,756	$ 53,262
Other income	849	1,337
Total revenues	59,605	54,599
Income/(loss) before taxes
Total income before taxes	13,922	14,822
U.S. Business segment [Member]
Revenues
Advisory fees	55,518	51,026
Other income	883	1,312
Total revenues	56,401	52,338
Income/(loss) before taxes
Total income before taxes	17,371	17,908
International Business Segment [Member]
Revenues
Advisory fees	3,238	2,236
Other income/(loss)	(34)	25
Total revenues	3,204	2,261
Income/(loss) before taxes
Total income before taxes	$ (3,449)	$ (3,086)