Segment Reporting - Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Revenues:
Total revenues	$ 65,485	$ 58,904
Total operating expenses	(54,802)	(45,683)
Other income/(expenses)
Interest expense	(2,892)
Interest income	779	962
Gain on revaluation of deferred consideration	4,404
Impairment	572
Other gains/(losses), net	(4,627)	(261)
Income/(loss) before taxes	7,775	13,922
Advisory Fees [Member]
Operating Revenues:
Total revenues	64,840	58,456
U.S. Business segment [Member]
Operating Revenues:
Other income	106	147
Total revenues	42,623	55,665
Total operating expenses	(37,176)	(39,030)
Other income/(expenses)
Interest expense	(192)
Interest income	779	962
Impairment	(572)
Other gains/(losses), net	145	(226)
Other income/(expenses)	160	736
Income/(loss) before taxes	5,607	17,371
U.S. Business segment [Member] | Advisory Fees [Member]
Operating Revenues:
Total revenues	42,517	55,518
International Business Segment [Member]
Operating Revenues:
Other income	539	301
Total revenues	22,862	3,239
Total operating expenses	(17,626)	(6,653)
Other income/(expenses)
Interest expense	(2,700)
Gain on revaluation of deferred consideration	4,404
Other gains/(losses), net	(4,772)	(35)
Other income/(expenses)	(3,068)	(35)
Income/(loss) before taxes	2,168	(3,449)
International Business Segment [Member] | Advisory Fees [Member]
Operating Revenues:
Total revenues	$ 22,323	$ 2,938