Segment Reporting - Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Revenues:
Total revenues	$ 66,293	$ 74,775	$ 131,778	$ 133,679
Total operating expenses	(54,382)	(60,244)	(109,184)	(105,927)
Other income/(expenses)
Interest expense	(2,910)	(2,356)	(5,802)	(2,356)
Interest income	818	612	1,597	1,574
(Loss)/gain on revaluation of deferred consideration	(4,037)	9,898	367	9,898
Impairment			572
Other gains and losses, net	284	(501)	(4,343)	(762)
Income/(loss) before income taxes	6,066	22,184	13,841	36,106
Advisory Fees [Member]
Operating Revenues:
Total revenues	65,627	73,778	130,467	132,234
U.S. Business segment [Member]
Operating Revenues:
Other income	76	162	182	309
Total revenues	43,146	53,093	85,769	108,758
Total operating expenses	(36,407)	(42,638)	(73,583)	(81,668)
Other income/(expenses)
Interest expense	(194)	(173)	(386)	(173)
Interest income	818	612	1,597	1,574
Impairment			(572)
Other gains and losses, net	(54)	(66)	91	(292)
Other income/(expenses)	570	373	730	1,109
Income/(loss) before income taxes	7,309	10,828	12,916	28,199
U.S. Business segment [Member] | Advisory Fees [Member]
Operating Revenues:
Total revenues	43,070	52,931	85,587	108,449
International Business Segment [Member]
Operating Revenues:
Other income	590	835	1,129	1,136
Total revenues	23,147	21,682	46,009	24,921
Total operating expenses	(17,975)	(17,606)	(35,601)	(24,259)
Other income/(expenses)
Interest expense	(2,716)	(2,183)	(5,416)	(2,183)
(Loss)/gain on revaluation of deferred consideration	(4,037)	9,898	367	9,898
Other gains and losses, net	338	(435)	(4,434)	(470)
Other income/(expenses)	(6,415)	7,280	(9,483)	7,245
Income/(loss) before income taxes	(1,243)	11,356	925	7,907
International Business Segment [Member] | Advisory Fees [Member]
Operating Revenues:
Total revenues	$ 22,557	$ 20,847	$ 44,880	$ 23,785